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Exploring geography and multi-level factors associated with disparities in HPV vaccination among Latino adolescents in Los Angeles County
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Exploring geography and multi-level factors associated with disparities in HPV vaccination among Latino adolescents in Los Angeles County
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Content
EXPLORING GEOGRAPHY AND MULTI-LEVEL FACTORS ASSOCIATED WITH
DISPARITIES IN HPV VACCINATION AMONG LATINO ADOLESCENTS IN LOS
ANGELES COUNTY
by
Bibiana Martinez
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERISTY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PREVENTIVE MEDICINE)
May 2023
Copyright 2023 Bibiana M. Martinez
ii
DEDICATION
I dedicate this work to Rosalba Patiño de Argüello (QEPD), my maternal grandmother. She has
been the North Star in my life and instilled in me the importance of compassion, sacrifice, and
education.
iii
ACKNOWLEDGEMENTS
I would not have been able to complete this work without the support of a strong network of
family, friends, and mentors who have guided and maintained me through this process. First and
foremost, I want to thank my husband Justin Shahbaz, my life partner and bedrock. You believed
in this dream when I was too afraid to believe in it myself, and then supported me financially and
emotionally through this journey every single day. Thank you for believing in me unconditionally,
always.
This accomplishment would have been impossible without a lifetime of support from my parents,
Leila Argüello and Rodrigo Martinez, who committed themselves from the very start of my life to
giving me the best education they could afford and making sure I learned English. My mother first
taught me how to read and then spent my childhood making sure I fell in love with books and
learning; my father drilled in me the importance of discipline and sacrifice in accomplishing
anything worthwhile. They instilled in me intellectual curiosity; taught me the value of academic
success; and encouraged me to have big dreams. Gracias Papi y Mami por enseñarme que lo
que se siembra, se cosecha.
I also want to acknowledge my family members in Colombia and Miami who surrounded me with
love and celebrated all my accomplishments through the years. Crucially, I would like to thank my
uncle and godfather, Armando Martinez, whose personal sacrifice opened a legal pathway for me
to immigrate to this country and made this beautiful dream possible. I would equally like to thank
my in-laws, Deborah and Said Shahbaz, for treating me like a daughter, giving me the love and
space I needed to complete this difficult work, and forgiving my frequent absences from family
outings during my time at USC.
iv
I have relied on the encouragement and support of a wonderful group of friends to surmount every
fear and obstacle I have faced during these past four years. I want to thank my brother in this
program, Steven De La Torre, for supporting me, listening to me, and taking every single one of
my panicked calls. Thank you to Carol Ochoa, Ixel Hernandez, Cynthia Begay, Patricia Escobedo,
Carlos Garcia, and Robert Garcia for being my tribe as well as an unending well of support,
guidance, motivation, and validation.
I want to acknowledge Kathleen Riggs, Nicholas Gallagher, and Ziyad Al Munifi who have been
my family in this country and have held me up when I could not stand on my own; and Cathy
Emmet for her loving guidance. I want to especially thank Victoria Floor for being my cheerleader
during the past 22 years, for never once doubting my abilities and inner strength, and for
encouraging me to pursue a career in public health in the first place.
Within USC, I would like to acknowledge and thank Laura Thompson for accommodating my
innumerable anxious meeting requests, and then patiently holding my hand as I found my footing
in geospatial research in general and ArcGIS Pro in particular. Thank you to Rosa Barahona and
Marlene Caldera, who intervened many times to ensure I got the time I needed from my mentors.
And thank you to Carolina Aristizabal for your feedback, your warmth, and for making me a little
less homesick.
Lastly, I would like to thank like my dissertation committee for supporting me over the past year
during the development, proposal, and execution of the research presented in this dissertation.
Thank you to my Chair, Dr. Myles Cockburn, for mentoring me with rigor and humor, and always
stepping in with kind words of encouragement and advice when things became overwhelming. I
deeply appreciate the hours you have gifted me to discuss my research, my career, and cat
behavior. Thank you Dr. Lourdes Baezconde-Garbanati for your invaluable personal mentorship;
v
for making me a part of your research family; and for taking me under your wing during difficult
transitions. Dr. Trevor Pickering, I will always be grateful for your generosity in time and attention
in reviewing the minutiae of the data and analyses used in this research. Thank you to Dr. Jennifer
Tsui for your thorough feedback and attention to detail in reviewing this work, as well as all prior
research products you have supported me in developing. And thank you to Dr. Lawrance Palinkas
for your incisive questions and knowledgeable suggestions as I have progressed through the
research and writing of the studies in this dissertation.
vi
TABLE OF CONTENTS
DEDICATION .............................................................................................................................. ii
ACKNOWLEDGEMENTS .......................................................................................................... iii
LIST OF TABLES ........................................................................................................................ x
LIST OF FIGURES .................................................................................................................... xi
ABSTRACT ............................................................................................................................... xii
CHAPTER 1: Introduction to HPV Vaccination in the United States, with Special Attention to
Latino Populations in Los Angeles County ................................................................................. 1
Public Health Impact of Human Papillomavirus and Disparities Involving Latinos................... 1
HPV Vaccine History and Current Use Protocols ................................................................... 2
Disparities in HPV Vaccine Uptake......................................................................................... 3
The Research Gap ................................................................................................................. 3
Organization of Remaining Dissertation ................................................................................. 5
CHAPTER TWO: Using the Social Ecologic Model to Understand the Multi-level Factors
Impacting HPV Vaccine Uptake among Parents of Adolescents. ............................................... 7
Theoretical Framework: The Social Ecologic Model ............................................................... 7
Multi-level Factors Associated with HPV Vaccination Among Adolescents ............................. 8
Individual Level Factors ...................................................................................................... 8
Interpersonal Level Factors ...............................................................................................10
Community Level Factors ..................................................................................................12
Conceptual Model for Dissertation Research Studies ............................................................14
Dissertation Studies, Aims, and Hypotheses .........................................................................15
vii
CHAPTER 3: Study 1: A Sub-county Examination of Community-level Factors Impacting HPV
Vaccination Uptake Across Los Angeles County .......................................................................18
ABSTRACT ...........................................................................................................................18
BACKGROUND ....................................................................................................................20
METHODS ............................................................................................................................23
Unit of Analysis & Eligibility Criteria ...................................................................................23
Data Sources ....................................................................................................................24
Analytic Approach .............................................................................................................26
Sensitivity Analysis ............................................................................................................28
RESULTS .............................................................................................................................30
HYPOTHESIS 1 A .............................................................................................................31
HYPOTHESIS 1 B .............................................................................................................43
DISCUSSION ........................................................................................................................50
Strengths and Limitations ..................................................................................................58
Study Implications .............................................................................................................61
CHAPTER 4: Study 2: Individual and Interpersonal Factors Driving Adolescent HPV Vaccine
Uptake among Latinos in a High-Risk Community for Cervical Cancer .....................................62
ABSTRACT ...........................................................................................................................62
BACKGROUND ....................................................................................................................64
METHODS ............................................................................................................................66
Data Source ......................................................................................................................67
Study Variables .................................................................................................................69
Analytic Approach .............................................................................................................73
viii
RESULTS .............................................................................................................................74
Sample description ............................................................................................................74
Acculturation Levels ..........................................................................................................77
Regression Models ............................................................................................................80
Index .................................................................................................................................84
Effect Modification .............................................................................................................84
DISCUSSION ........................................................................................................................86
Limitations and Study Implications ....................................................................................89
CHAPTER 5: Study 3: Implementing GIS-Based Multi-Criteria Decision Analysis to Optimize
Delivery of HPV Vaccine Interventions among Latino Communities in Los Angeles ..................92
ABSTRACT ...........................................................................................................................92
BACKGROUND ....................................................................................................................94
METHODS ............................................................................................................................96
Unit of Analysis and Eligibility Criteria ................................................................................96
Analytic Approach .............................................................................................................97
Data Sources ....................................................................................................................98
Potential Reductions in Cancer Burden ........................................................................... 100
RESULTS ........................................................................................................................... 102
Area Characteristics ........................................................................................................ 102
MCDA – Components and Final Score ............................................................................ 103
Population Preventable Fraction ...................................................................................... 106
Dissemination of Study Results ....................................................................................... 106
DISCUSSION ...................................................................................................................... 107
ix
CHAPTER 6: Discussion, Implications and Future Directions for HPV Vaccination Among
Diverse Latino Communities. .................................................................................................. 111
SUMMARY OF FINDINGS .................................................................................................. 111
IMPLICATIONS ................................................................................................................... 113
OVERALL DISSERTATION LIMITATIONS ......................................................................... 114
FUTURE RESEARCH DIRECTIONS .................................................................................. 116
REFERENCES ....................................................................................................................... 118
APPENDIX 1. Los Angeles County neighborhoods with overlap with high-risk areas. ............. 140
APPENDIX 2. Study 3 Questionnaire with Interviewer and Coder Instructions ........................ 143
x
LIST OF TABLES
Table 1. Study 1 Measures .......................................................................................................24
Table 2. Demographic characteristics of ZCTAs in Los Angeles County ...................................32
Table 3. Linear regression model results of percent of HPV vaccine initiation ...........................33
Table 4. Pearson Correlation Coefficients. ................................................................................34
Table 5. Multilinear regression model ........................................................................................35
Table 6. Multilinear regression model using predictors categorized as tertiles...........................36
Table 7. Multilinear regression model replacing Uninsurance with Public Insurance measure. ..38
Table 8. Multivariable linear regression model only including variables with significant
associations .....................................................................................................................38
Table 9. Model diagnostics for OLS and GWR. .........................................................................39
Table 10. Los Angeles neighborhoods at high risk of cervical cancer. .......................................49
Table 11. Study 2 Measures .....................................................................................................68
Table 12. Study 2 sample characteristics. .................................................................................75
Table 13. Study 2 sample characteristics by acculturation level. ...............................................78
Table 14. Logistic regression models of adolescent HPV vaccine uptake. ................................81
Table 15. Pearson Correlation Coefficients of proposed predictors ...........................................83
Table 16. Stratified multivariable logistic regression models of HPV vaccine uptake,
including variables significantly associated with HPV vaccine uptake at p<0.1 in
bivariate models and the VIF for each predictor. ............................................................85
Table 17. Characteristics of Los Angeles County ZCTAs, ZCTAs with >60% Latino
populations, and ZCTAs with >60% Latino populations at high-risk for cervical cancer. 102
Table 18. Factor pattern and communality estimates for Factor 1 from PCA . ......................... 104
xi
LIST OF FIGURES
Figure 1. The Social Ecologic Model in HPV Vaccination ........................................................... 7
Figure 2. Conceptual Model of Dissertation Studies ..................................................................15
Figure 3. 5-year Survival Rates for Cervical Cancer in Los Angeles County by stage of
diagnosis, 2012-2018 ......................................................................................................29
Figure 4. Percent of yearly HPV vaccine initiation rate in Los Angeles County, 2007-2021 .......31
Figure 5. Scatterplots of ZCTA-level HPV Vaccination Rate with Percent Latino and
Percent Non-US Born . ...................................................................................................37
Figure 6. GWR Regression Coefficients for percent yearly Tdap initiation rate..........................40
Figure 7. GWR Regression Coefficients for percent of Latino population. .................................41
Figure 8. GWR Regression Coefficients for percent uninsured population. ...............................42
Figure 9. GWR Regression Coefficients for percent non-US born population. ...........................43
Figure 10. Threshold values for cervical cancer clusters. ..........................................................44
Figure 11. ZCTAs in LAC overlapping a cervical cancer cluster. ...............................................45
Figure 12. Map of regression residuals of the relationship between HPV vaccine uptake
and cervical cancer clusters. ..........................................................................................46
Figure 13. LAC ZCTAs at high risk for cervical cancer. .............................................................48
Figure 14. Hot and cold spots of cervical cancer incidence for all race/ethnicities in Los
Angeles County ..............................................................................................................68
Figure 15. HPV Vaccine Initiation among adolescents in Los Angeles County. .........................68
Figure 16. Screenshot of the “Optimizing Adolescent HPV Vaccination at LA County
Latino Communities at High Risk for Cervical Cancer” online dashboard. .................... 107
xii
ABSTRACT
Introduction: In the United States, Latinas are 43% more likely to be diagnosed with cervical
cancer than non-Hispanic white women, and 20% more likely to die as a result, with nearly all
cervical cancers attributed to human papillomavirus (HPV) infection. Latinos account for 49% of
the population in Los Angeles (LA) County, and data from the 2018 Los Angeles County Health
Survey reveal that Latino adolescents in the county have lower vaccination rates than non-
Hispanic whites (45% vs. 54%). A more granular, community-centered exploration of the
multilevel factors associated with HPV vaccination in Latino communities is needed to
understand the strategies necessary to improve the disproportionate cervical cancer burden in
this group.
Methods: Geographic weighted regression was used to examine the relationship (including
assessing spatial correlation) between ZIP code tabulation area (ZCTA) level factors (i.e.,
poverty, uninsurance, nativity, Latino ethnicity, Tdap uptake, residential segregation) and ZCTA
level HPV vaccine uptake (from the California Immunization Registry) among adolescents (ages
9-17) residing in Los Angeles County; areas of the county within a hotspot and with low HPV
vaccination rates were determined to be at high risk for cervical cancer (Study 1). Multivariable
logistic regression was used to identify the personal (e.g., acculturation, knowledge) and
interpersonal (e.g., medical mistrust, provider recommendation) factors impacting HPV vaccine
uptake among Latino parents of adolescents residing in a community with high cervical cancer
incidence and low HPV vaccine uptake; we also explored how these varied by acculturation
level (Study 2). Finally, GIS-based Multi-Criteria Decision Analysis (MCDA) was used to
incorporate both community, interpersonal, and individual level factors to identify clinics in
Latino communities with largest potential for HPV vaccination uptake improvements; a
population preventable fraction quantified the improvements in cervical cancer burden by
implementing interventions to improve HPV vaccination in high-risk Latino communities (Study
3).
xiii
Results: Study 1 found that HPV vaccination uptake among adolescents in Los Angeles County
varied broadly, and that the average rate of uptake in the County using CAIR estimates was well
below national estimates. Geographic weighted regression models identified ZCTA-level Tdap
vaccine uptake as the strongest positive correlate of HPV vaccination; and found that
adolescent HPV vaccination was positively associated with ZCTA-level nativity, Latino ethnicity,
and insurance in some Los Angeles County ZCTAs, while being negatively associated with
them in other areas. Study 2 found that lack of a provider recommendation for the HPV vaccine
and male parental/caregiver sex were negatively associated with HPV vaccine uptake among
parents of Latino adolescents residing in a community at high risk for cervical cancer, after
controlling for all other predictors in the model. We also found that parental acculturation
significantly modified the relationship between provider recommendations and adolescent HPV
vaccination, and that the positive impact of a provider recommendation to vaccinate on HPV
vaccine uptake was more pronounced among high acculturated Latino parents. Study 3
identified 17 VFC clinics located in high-risk Latino communities in Los Angeles County, and
found that MCDA scores ranged between 61 and 1668. The largest variation in the component
scores were distance from the clinics to the nearest cervical cancer hot spot, and proportion of
late-stage cases of cervical cancer in the ZCTA where the clinic was located. Population
preventable fractions found reductions in cervical cancer incidence 31% greater resulting from
implementing an intervention to improve HPV vaccination in clinics located within these
communities, compared to locating them in clinics outside the selected ZCTAs. Lastly, we
utilized a publicly available GIS-based online dashboard to visualize our findings as a first step
in disseminating our study results.
Conclusion: The exploration of multilevel factors associated with HPV vaccine uptake in
vulnerable communities is critical to identifying actionable approaches for improving HPV
vaccination in populations most in need for long-term cervical cancer prevention strategies and
decrease the disproportionate burden of HPV-associated cancers among Latinos.
1
CHAPTER 1: Introduction to HPV Vaccination in the United States, with Special Attention to
Latino Populations in Los Angeles County
Public Health Impact of Human Papillomavirus and Disparities Involving Latinos
Human Papillomavirus (HPV) is the most common sexually transmitted infection. While
approximately 90% of HPV infections are temporary, asymptomatic and resolve on their own,
1
for some individuals HPV infection can lead to anogenital warts and cancers of the cervix,
vagina, vulva, penis, anus, and oropharynx.
1,2
HPV infection is responsible for over 90% of
cervical and anal cancers and approximately 70% of cancers of the oropharynx, penis, vagina,
and vulva.
1
The financial burden of HPV-associated cancers in the United States is substantial,
with medical costs estimated to be over $700 million dollars.
3
Cervical cancer is the leading HPV-associated cancer in the world with over half a million cases
each year;
4
nearly all cervical cancers are attributed to human papillomavirus (HPV) infection.
2
Cervical cancer disproportionately and persistently impacts Latinas. In the United States,
Latinas are up to 43% more likely to be diagnosed with cervical cancer than non-Hispanic white
women, and 20% more likely to die as a result.
5,6
Latinas are also more likely to be diagnosed
with cervical cancer at later stages and experience worse disease progression than non-
Hispanic White women,
7
resulting in more costly and complicated treatment regimens and
reduced odds of survival.
8
There is broad geographic variation in HPV-related cancer incidence
9-12
both regionally and
across the country.
13
Local level data show disproportionately higher cervical cancer burden
among some LAC geographies aligned with Latino enclaves,
11
suggesting area-based factors
impacting risk of HPV disease among Latinos in Los Angeles County.
14
2
HPV Vaccine History and Current Use Protocols
Vaccination against HPV is one of the most effective strategies for preventing cervical
cancer.
15,16
Three different vaccines have been approved for the prevention of HPV infection in
the United States (2vHPV, 4vHPV, and 9vHPV), but since 2017 the only one available for use is
9vHPV, known as Gardasil© 9 and manufactured by Merck & Co, Inc.
17
There have been
significant declines in the HPV strains targeted by the HPV vaccine in the decade since
vaccination was introduced in the U.S.
1
as well as reductions in anogenital warts and HPV-
associated cancers among both women and men.
18-24
The HPV vaccine is so effective in
preventing in the types of HPV associated with cervical cancer that its eradication in the United
States in now an achievable goal.
25,26
While the Center for Disease Control and Prevention’s (CDC) Advisory Committee on
Immunization Practices (ACIP) currently recommends routine HPV vaccination among
adolescents of both sexes ages 11-12, with expanded eligibility for individuals ages 9-45,
15
guidelines for HPV vaccination have changed multiple times since the vaccine was first licensed
in 2006. From 2007 through 2019, ACIP modified its recommendations seven times to include
new populations (males, immunocompromised, and transgender individuals), vaccine
formulations (4vHPV, 2vHVP, 9vHPV), age groups, and dosing schedules (2 vs. 3 doses).
15,27-32
These changes have produced confusion among parents and community members, acting as a
barrier for uptake among some groups,
33
and have been manipulated by some political actors to
highlight uncertainty and sow controversy, potentially amplifying confusion and parental
concerns about the HPV vaccine.
34
3
Disparities in HPV Vaccine Uptake
Even though the HPV vaccine provides nearly 100% protection against the types of HPV
contained in the vaccine,
15
and despite its broad coverage through different insurance
mechanisms,
35
as of 2021 only 62% of adolescents in the U.S. ages 13-17 years had completed
the HPV vaccine series.
36
There are disparities in uptake of the HPV vaccine, with a 2019
systematic review finding higher initiation but lower completion of the HPV vaccine series
among ethnic/racial minorities.
37,38
However, disruptions to healthcare delivery and missed
doses of HPV vaccination during the COVID-19 pandemic, which impacted racial/ethnic
minorities disproportionately, may have substantially affected some of these trends.
15,39,40
While national averages estimate that HPV vaccine initiation is highest among Latino
adolescents (72.2%),
41
studies of Latino parents report adolescent uptake rates ranging from
15-55%,
8,42,43
with broad regional and geographic variability.
44
Similarly, a review of studies of
adolescent vaccination among children of Latino immigrant parents found uptake at
approximately 30%.
45
There is also substantial variation in uptake across Latino subgroups in
the U.S.
46
The COVID-19 pandemic has severely impacted healthcare utilization
47
and led to sharp
declines in use of cancer screening and preventive services,
48-50
including adolescent
vaccinations.
40
As racial/ethnic minority communities have been disproportionately impacted by
COVID-19,
51
some of these delays in cancer screening have disproportionately impacted
Latinos.
52
The Research Gap
There are broad, understudied disparities in burden of cervical cancer and uptake of the HPV
vaccine in sub-county geographies. Very little research to date has focused on understanding
4
how community level factors impact HPV vaccination at sub-county geographies or how these
factors differ across communities.
53
This is especially salient in Latino communities, where
sociodemographic and healthcare access barriers may differ widely by immigration pathway,
acculturation, and poverty status.
54-59
Furthermore, assessment of geographic disparities in HPV
vaccination at sub-county levels has been limited, especially among Latino populations.
53
We
must identify local community-level variability in the factors impacting HPV vaccination in order
to design and deliver culturally responsive interventions where they are most needed and can
be most effective.
While some literature has explored acculturation, language use, and other sociodemographic
characteristics as predictors of HPV vaccine uptake among Latino sub-groups, no research to
date has focused on identifying the factors impacting HPV vaccination among Latino
communities at higher risk of cervical cancer because of their residence in areas with high
cervical cancer burden and low HPV vaccine uptake, or on understanding the individual and
interpersonal factors impacting HPV vaccine uptake among Latino parents of adolescents
residing in such communities.
COVID-19 has heightened vaccine decision making,
60-63
but it is unclear whether or how the
pandemic has impacted HPV vaccine hesitancy among Latino communities. Exploring the
relationship between uptake of COVID-19 and HPV vaccines at small area geographies is a
necessary first step in clarifying this relationship, which could inform planning for context-
responsive HPV vaccination strategies.
Furthermore, no research to date has leveraged Geographic Information Systems (GIS) to
explore how the location of clinics currently offering HPV vaccination services in Latino
5
communities can be examined and ranked to identify optimal sites at which to implement
interventions to improve HPV vaccine uptake among Latino adolescents.
The multi-level, cross sectional dissertation studies described in this proposal will perform
secondary analyses of community, interpersonal, and individual levels of data to examine how
factors at different levels of influence impact cervical cancer burden and HPV vaccination in
Latino communities, and how to best use this information to locate prevention interventions
where they can be most effective.
It is noteworthy that all of the research described in this dissertation occurred during years 2021-
2023, while the COVID-19 pandemic was in effect. In particular, this could have impacted the data
collection of the primary data used in Study 1, and the data collection activities in Study 3.
Organization of Remaining Dissertation
The remaining chapters in this dissertation are organized as follows. Chapter 2 will present a
theoretical framework which we will use to understand the multi-level factors impacting
adolescent HPV vaccination and will present a review of the literature on the factors impacting
HPV vaccine uptake among parents of adolescents, with a special focus on Latino parents.
Chapter 3 will describe an exploration of how factors at the zip code tabulation area (ZCTA)
level impact HPV vaccination, and whether there is spatial variation in those relationships
(Study 1). Chapter 4 will focus on a community with high incidence of cervical cancer and low
HPV vaccine uptake and explore the individual and interpersonal factors associated with HPV
vaccine uptake among Latino parents of adolescents (Study 2). Chapter 5 will then describe
how the results of the research proposed in Chapters 3 and 4 was incorporated into an online
dashboard displaying the results of a GIS-based Multi-Criteria Decision Analysis that identifies
which clinics offering HPV vaccine services are most optimally located to incorporate
6
interventions to improve HPV vaccine uptake (Study 3) in Latino communities in Los Angeles
County. Chapter 6 presents an integrated discussion of the three study results, notes limitations,
and highlights the potential impact of this dissertation research.
7
CHAPTER TWO: Using the Social Ecologic Model to Understand the Multi-level Factors
Impacting HPV Vaccine Uptake among Parents of Adolescents.
Theoretical Framework: The Social Ecologic Model
Multiple complex factors, operating at different spheres of influence, can impact HPV
vaccination behavior.
64-66
To understand disparities in HPV vaccination and effectively address
the disproportionate burden of cervical cancer among Latinos, we need a framework that can
encompass and integrate multiple factors, operating at multiple levels, in our understanding of
HPV vaccination behavior.
The Social Ecologic Model was introduced and formalized by Bronfenbrenner in the 1970s and
80s to describe the impact of multiple community and environmental factors on the familial
context in which human development occurs.
67,68
This framework has been further adapted and
operationalized for the study of health promotion,
69,70
by conceptualizing health behaviors as
existing within broader social and environmental systems with which they interact, and being
impacted by factors operating at four levels: individual, interpersonal, community, and society
levels.
69
The Social Ecologic Model has been used
to explain the factors associated with HPV
vaccination among adolescents in the
US.
65,71
Mansfield and colleagues’
conceptualization included both
adolescent and parents beliefs about HPV
vaccination and sociodemographic
characteristics as part of the individual
Figure 1. The Social Ecologic Model in HPV Vaccination.
Modified from Mansfield et al.
61
8
level; healthcare provider, family, and peer influences within the interpersonal level; accessibility
to healthcare, geographic characteristics, and community socioeconomic status within the
community level; and HPV vaccination policies within the societal level.
65
Multi-level Factors Associated with HPV Vaccination Among Adolescents
As HPV vaccination is routinely recommended for adolescents, parents and caregivers are
crucial stakeholders in all HPV vaccination decision-making processes; understanding how
factors at each level of the Social Ecologic Model impact HPV vaccine uptake among parents of
adolescents is therefore of paramount importance. An abundant body of literature has explored
this topic, including both empirical studies and systematic reviews. The following section
provides a summary of this literature, organized by the first three levels of the Social Ecologic
Model (Individual, Interpersonal, and Community), with special emphasis on parents of Latino
adolescents. As this dissertation research will focus on communities and geographies within Los
Angeles County, factors impacting HPV vaccination at the Society level are outside of the scope
of this review.
Individual Level Factors
Knowledge, Attitudes, and Beliefs
Parental awareness and knowledge about the HPV vaccine, as well as perceived susceptibility
to HPV and perceived benefits, effectiveness, and safety of the HPV vaccine have all been
positively associated with HPV vaccine uptake.
65,66
Lack of knowledge and negative attitudes
about the HPV vaccine have similarly been associated with lower uptake.
65,66
Of concern, a
trend of decreasing awareness about the HPV vaccine has been recently identified among all
parents, but this trend is especially strong among racial/ethnic minority groups.
72
9
Parental hesitancy towards vaccination has become a key factor in our understanding of
immunization behavior among minority communities. However, HPV vaccine hesitancy among
Latino parents is not well understood, with reports of both positive vaccination attitudes towards
pediatric vaccinations in general
8,73,74
and hesitancy despite a provider recommendation to
vaccinate.
8
Furthermore, positive attitudes towards the HPV vaccine have not always been
associated with HPV vaccine uptake among Latino parents.
42,45
There are conflicting reports about knowledge about HPV, HPV-associated cancers, and the
HPV vaccine in Latino communities, with some studies reporting low overall knowledge
8,45,75-80
and others reporting high levels of information related to HPV.
8,81,82
Nevertheless, studies with
multi-ethnic samples have found that Latinas are less likely to have heard about HPV
vaccination than non-Hispanic White women
8
. Knowledge of the HPV vaccine is especially low
among Latina immigrants.
45,81,83
The most commonly reported barriers to HPV vaccination among Latino parents are concerns
that vaccinating their children against HPV will condone sexual activity, concerns about vaccine
safety and side effects, and low perceived risk of HPV infection.
8
Acculturation
There are conflicting reports about the impact of acculturation on HPV vaccine uptake among
Latinos. Low acculturation levels
9,10
and poor English proficiency
65,66
have been identified as
barriers to HPV vaccination among some Latino parents. Among Latino immigrants, less
acculturated and Spanish-speaking parents were less likely to be aware of the HPV vaccine.
45,84
Conversely, longer length of stay in the US has been associated with higher HPV vaccination,
and daughters of Latina immigrant mothers with high acculturation were found to be more likely
10
to have received the HPV vaccine.
45
However, some studies have found that Latina mothers
with lower English proficiency had higher levels of knowledge than those with higher English
proficiency,
85
and that lower acculturation is associated with higher odds of HPV vaccine series
completion.
38,46
Additionally, Stevens and colleagues found that preferred language, which is a
commonly used measure of acculturation, was not significantly associated with HPV vaccine
uptake.
45
Sociodemographic Characteristics
Being Latino, higher poverty status, and being insured have been associated with increased
HPV vaccine initiation.
8,39,45,65
Nevertheless, lower rates of HPV vaccine series completion have
been found among Latino and African American adolescents.
65
Associations have also been
identified between HPV vaccine series completion and maternal education.
8
Younger
adolescents are less likely to have initiated the HPV vaccine series, and lower uptake has also
been observed among children living in households with multiple siblings.
65,66
Interpersonal Level Factors
Relationships with Providers
Parental report of a provider recommendation to vaccinate against HPV is the most statistically
significant predictor of adolescent HPV vaccination.
65,66
Lack of a provider recommendation for
HPV vaccination has been consistently associated with lower HPV vaccine uptake among
Latino parents.
8,75,84,86
Moreover, various studies have found that Latinos are less likely to
receive a provider recommendation to vaccinate against HPV compared to non-Hispanic
Whites.
8
11
The role of trust in healthcare institutions and providers, and its association with HPV vaccine
uptake among parents and guardians of Latino adolescents has been examined thoroughly.
87
Latino parents have been found to have more positive, trusting relationships with medical
providers, and many point to their doctors as their most trusted source of information about the
HPV vaccine;
8,45,73,87,88
this is especially true among Spanish-speaking parents.
89
Still, reports of
medical mistrust among some Latino groups also exist in the literature.
90-93
Relationships with Family and Peers
Among parents of adolescents at large, positive opinions from family and friends about the HPV
vaccine is positively associated with HPV vaccine uptake.
65
Familial and social relations also
play a role in decisions made by Latino parents related to HPV vaccination. Belief that other
parents had vaccinated their children against HPV
8
and the belief that a child’s father approved
of the HPV vaccine have been found to be a significant predictor of uptake among children of
Latina mothers.
8
Similarly, familial decision-making was found to be predictive of HPV vaccine
uptake among children of immigrants.
66
Health information-seeking behavior can also impact HPV vaccine uptake among Latino
parents. Latinos who heard about HPV vaccination from doctors are more likely to discuss it
with others close to them than those who heard about HPV vaccination from the media,
8
and
social discussion about the HPV vaccine has been associated with perceived HPV vaccine
effectiveness.
8
Misinformation about the HPV vaccine
94-97
has been associated with poor HPV
vaccine uptake among parents of Latino adolescents.
12
Community Level Factors
Geographic disparities in the uptake of HPV vaccination are well documented, with lower
initiation reported in the Southern states, as well as among rural communities, and in non-
Metropolitan Statistical Areas.
33,39
Broad within-state regional variations in HPV vaccine uptake
have also been reported.
98
While our understanding of the area-based factors associated with
HPV vaccination has improved since they were first reported over a decade ago by Pruitt and
colleagues,
99
we still know little about the distribution of HPV vaccination in small-area, sub-
county geographies, or the factors associated with differential uptake among Latinos and other
vulnerable communities in such sub-county geographies.
53
Area-level Sociodemographic Factors
Area level poverty
65,99
and racial/ethnic composition
53,65
have been shown to impact HPV
vaccine uptake, but the direction of the association between area-level poverty and HPV
vaccine uptake has varied by region and by differing definitions of geographical areas.
37,53
Rurality and urbanicity have been found to impact adolescent uptake of HPV vaccines as well,
with adolescents living outside of metropolitan statistical areas (MSA) and those living in rural
areas having lower uptake of the HPV vaccine.
39,53
HPV-Associated Cancer Incidence
Adolescent girls living in states with high incidence and mortality from HPV-associated cancers
have been found to have both lower HPV vaccine series initiation and completion.
100
However,
little research exists examining the association between HPV-associated cancer incidence and
HPV vaccine uptake in sub-county geographies.
53
13
Healthcare Use and Access
Use of cancer screening services by mothers (Pap-Smears and mammography) or parental use
of influenza immunizations have been associated with increased HPV vaccine uptake in their
adolescents.
65,66,101
Adolescent use of preventive services in the previous year and uptake of
other adolescent vaccines have likewise been associated with higher rates of HPV vaccine
series initiation and completion.
65,66
Facility type has also been associated with HPV
vaccination, with private practices and facilities with pediatricians, gynecologists, and
vaccination provider having higher HPV vaccination rates.
65
With regards to distance, Tsui and
colleagues found no association between clinic proximity and HPV vaccine uptake.
102
Among Latino parents, factors such as vaccine cost, insurance coverage, clinic type, availability,
and time concerns
45,53,75,80,103,104
have been shown to impact HPV vaccination behavior. Some
Latinos have also reported lack of knowledge about where to get the HPV vaccine.
103
Clinic-Based Strategies to Improve HPV Vaccination. Substantial improvements in HPV
vaccination rates have been associated with a number of clinic-based strategies, such as high-
quality provider recommendations, provider reminders, the use of Immunization Information
Systems, standing vaccine orders, provider prompts for vaccine recommendation, and provider
assessment and feedback.
105-119
However, limited research has explored the effectiveness of
these strategies among Latino parents specifically. Patient reminders substantially improved
HPV vaccination among Spanish-speaking Latinos in New York City, but the intervention was
implemented in a community-setting.
120
A package of clinic-based interventions (including
practice champions, physician and staff trainings, provider prompts to vaccinate in via the
electronic medical record (EMR), and providing the vaccine free of charge) significantly reduced
the odds of missed opportunities for HPV vaccination, but the study focused on young Latinas
receiving care at a hospital-based obstetrics/gynecology practice.
121
Qualitative research has
14
identified increased staff knowledge and involvement, provider recommendations, bundling, a
supportive EMR system, as well as appointment reminders as being perceived by providers to
be associated with high HPV vaccine uptake among Latino patients.
104,122
Social Determinants of Health
Limited research has focused on the impact of social determinants of health (SDOH) on HPV
vaccine uptake, particularly among parents of adolescents. Lower measures of social cohesion
have been associated with lower HPV vaccination among young women.
123
High incidence of
cervical cancer in communities with a history of redlining
124
suggest unexplored associations
between residential segregation and cervical cancer prevention behaviors, like HPV vaccination.
The association of other social determinants of health, such as educational investment, housing
stability, food insecurity, and employment, and HPV vaccine uptake among parents of
adolescents remains unexplored,
123,125
but present a promising opportunity to understand and
address the health effects of systemic racism on Latino communities in the U.S.
Conceptual Model for Dissertation Research Studies
Guided by Mansfield’s
65
adaptation, our conceptual model will focus on the first three levels of
the
Social Ecological Model: community, relationship, and individual. Since our study focuses on
communities and geographies within LAC, higher level factors of influence (county, state,
country) will not be examined. The dissertation research described herein examines: how
community-level sociodemographic, cancer incidence, health care utilization and access, and
social determinant of health factors impact community-level HPV vaccination (Study 1); how
interpersonal (e.g. relationships with providers, family, and peers), and individual factors (e.g.
vaccine hesitancy, acculturation) impact HPV vaccination among Latino parents of adolescents
15
residing in communities with high cervical cancer incidence and low HPV vaccine uptake (Study
2); and how geospatial analyses can be implemented within Latino communities to optimize the
location of HPV vaccination interventions at existing clinics and incorporated into health
dissemination strategies targeting community stakeholders (Study 3).
Dissertation Studies, Aims, and Hypotheses
Study 1: A sub-county examination of community-level factors impacting HPV
vaccination uptake across Los Angeles County
Study 1 utilizes ZCTA-level HPV vaccination rates among 9–17-year-olds, area-level cervical
cancer incidence, COVID-19 vaccination uptake, and sociodemographic factors from multiple
data sources to examine community level factors associated with HPV vaccination in LAC to
identify communities at highest risk for cervical cancer.
Figure 2. Conceptual Model of Dissertation Studies
16
Aim 1: Identify communities at high risk for cervical cancer and examine the community-level
factors associated with low HPV vaccination in Los Angeles County.
Hypothesis 1a: ZCTAs with high proportions of residents living below poverty, foreign-born,
Latino, without insurance coverage, and residential segregation will have lower ZCTA level HPV
vaccine initiation, compared to ZCTAs with lower proportion of residents living below poverty,
foreign-born, Latino, without insurance coverage, and residential segregation.
Hypothesis 1b: There will be an inverse relationship between cervical cancer incidence hotspots
and HPV vaccination rates among ZCTAS in LAC.
Hypothesis 1c: ZCTAs with low adolescent HPV vaccine uptake will also have low adolescent
COVID-19 vaccine uptake.
Study 2: Exploring the individual and interpersonal factors driving adolescent HPV
vaccine uptake among Latinos residing in a community at high risk for cervical cancer.
Study 2 includes a secondary analysis of survey data from “Addressing HPV vaccine hesitancy
in regions with low adolescent HPV vaccine uptake”,
43
an NCI-funded study on HPV vaccine
hesitancy in Los Angeles to examine individual and interpersonal factors driving HPV
vaccination of Latino parents of adolescents in a high cervical cancer risk area.
Aim 2: Identify the interpersonal and individual level factors associated with low HPV
vaccination uptake among Latinos residing in communities with high cervical cancer risk (as
defined in Study 1).
Hypothesis 2: Latino parents reporting multiple barriers to HPV vaccination will have lower odds
of having an adolescent who initiated the HPV vaccine series.
Study 3: Implementing GIS-Based Multi-Criteria Decision Analysis to optimize delivery of
HPV vaccine interventions among Latino communities in Los Angeles
17
Using data from Study 1 and Study 2, a GIS-based Multi-Criteria Decision Analysis (MCDA) was
used to develop an online dashboard which identifies optimal vaccination clinics within Latino
communities in Los Angeles County to implement HPV vaccination interventions.
Aim 3: Identify optimal Latino communities with largest potential for HPV vaccination uptake
improvements through geographic site suitability techniques and dissemination strategies.
Hypothesis 3: Attributable risk reduction of cervical cancer will be more than 20% by
implementing evidence-based interventions to improve HPV vaccination at targeted clinics within
ZCTAs at high risk for cervical cancer (per Aim 1) with >60% of Latinos rather than at clinics in
ZCTAs with <60% Latinos.
18
CHAPTER 3: Study 1: A Sub-county Examination of Community-level Factors Impacting HPV
Vaccination Uptake Across Los Angeles County
ABSTRACT
Background: While geographic disparities in adolescent Human Papillomavirus vaccination
have been documented, little is known about the factors that impact low area-based HPV
vaccination at subcounty levels, or whether these relationships vary within Los Angeles County
(LAC). Similarly, we have limited understanding about the relationship between area-level HPV
vaccine uptake and cervical cancer clustering within Los Angeles ZIP code tabulation areas
(ZCTAs).
Methods: Linear regression models explored the associations between ZCTA-level poverty,
insurance, nativity, and Latino ethnicity and yearly HPV vaccination rate per hundred among
adolescents ages 9-17 in LAC, using data from the American Community Survey (2015-2019)
and California Immunization Registry (2007-2021). Regression residuals were examined for
spatial autocorrelation using Global Moran’s I; geographic weighted regression (GWR) was
performed to explore local relationships. Kernel Density Analysis was used to calculate cervical
cancer hot spots using data from the Los Angeles Cancer Surveillance Program (2006-2019);
logistic regression models explored the association between HPV vaccine uptake and cervical
cancer hot spots in LAC.
Results: ZCTA-level mean yearly rate of HPV vaccination in LAC during years 2007-2021 was
5.1% (SD=1.8%). A one-unit increase in Tdap uptake was associated with an average increase
in yearly HPV vaccination rate of 0.8 (p<0.01); a 10% increase in Latino population was
associated with a 0.09 mean increase in the yearly rate of HPV vaccination per hundred
(p<.01); and a 10% increase in uninsured population was associated with a mean 0.31 increase
19
in yearly HPV vaccination rate per hundred (p<.01). Meanwhile, a 10% increase in non-US born
population was associated with a 0.07 decrease in mean yearly HPV vaccination rate per
hundred (p<0.01). Global Moran’s I identified significant unexplained spatial autocorrelation in
the regression residuals (0.047, p<0.01). GWR results indicate non-stationarity in the modeled
relationships; local coefficients ranged from 0.65-0.98 for Tdap uptake; -0.008 – 0.030 for
percent of Latino population; -0.147 – 0.086 for percent uninsured population; and -0.041 –
0.045 for percent non-US born population. R
2
(0.96 to 0.98) and AIC (-2331.15 to -2483.49)
improved in the GWR compared to linear regression model. HPV vaccination was positively and
significantly associated with Cervical cancer hot spots (OR=1.90, p<0.01), but explained only a
small amount of the variation in cervical cancer hot spots (R
2
=0.13).
Discussion: GWR uncovered ZCTA-level variation in the association between HPV vaccination
and predictors explored. Notably, local coefficient ranges for ZCTA-level percent Latino,
uninsured, and non-US born populations extended into the opposite direction than the global
linear model estimates, meaning HPV vaccine initiation is positively associated with larger
Latino, uninsured, and non-US born populations in some ZCTAs of LAC, while being negatively
associated with them in other areas. Insight into associations at the subcounty level can allow
for effective implementation of interventions responsive to diverse needs of LAC populations.
Positive associations between cervical cancer hot spots and HPV vaccination could reflect a lag
in the effects of vaccination on disease incidence; further exploration of the factors associated
with cervical cancer hot spots is necessary.
20
BACKGROUND
Local Variation in HPV Vaccination Behavior
Geographic disparities in uptake of HPV vaccination are well documented.
37,39,53,98,126-130
In order
to understand the factors that can explain spatial variation in HPV vaccine uptake, most studies
have used multilevel linear regression techniques to model area-level factors impacting HPV
vaccine uptake, which do not account for the spatial relationships which may be present in the
data.
53
Instead, linear regression models capture overall trends in the relationships between
predictors and outcomes and assume that the spatial placement of the predictors does not
impact their relationship with the outcome variable. This discounts Tobler’s First Law of
Geography, which states that: “everything is related to everything else, but near things are more
related than distant things”, as well as our understanding of the effects of neighborhoods on
health outcomes and behaviors.
131-133
In terms of HPV vaccination, neighborhoods and other small area geographies can impact
uptake behavior through three overarching pathways; through the social environment (e.g.,
social norms related to vaccination, social capital and cohesion, information networks, and
instrumental support available among neighbors)
134
; through the contextual effects of residential
characteristics (e.g., quality of care provided by local vaccination providers, availability of clinic
appointments); and through characteristics of the built environment (e.g., location of vaccination
clinics, accessibility of public transportation).
53,123,133
While previous studies have identified numerous community-based factors impacting HPV
vaccination, they have done so at different geographic resolutions (e.g., state
98,130
, county
130
, US
region)
127-129,135
with mixed results,
53
and few have focused on factors impacting uptake at sub-
county geographies.
53
This has limited our understanding of the neighborhood and community-
level factors impacting HPV vaccination, hindering our ability to design local, evidence-based
21
interventions that can effectively target behavior change and lead to improvements in HPV
vaccination uptake.
Factors Impacting Area-Level HPV Vaccination
Notwithstanding the mixed results of previous area-level studies exploring HPV vaccine uptake,
several of the area-level factors identified to impact HPV vaccine uptake can guide our
exploration of sub-county level correlates of HPV vaccination. Uninsurance at the county and
health service region level was associated with lower uptake of the HPV vaccine in Texas.
136
Communities with majority Latino populations have been found to have higher rates of HPV
vaccine uptake; however, differences by nativity have not been examined at sub-county
geographies.
53,65,100
Area-based poverty at the county and state levels has been associated with
HPV vaccination rates, but the direction of the relationship identified has varied by region and by
area level studied (state, county, census block).
37,53,137-139
Furthermore, Thompson and colleagues looked at the impact of social determinants of health
(SDOH) on HPV vaccination, and found that measures of social cohesion were associated with
HPV vaccine uptake in women.
123
Krieger and colleagues found that high area-level incidence
of cervical cancer was associated with a history of area-level redlining in Massachusetts,
124
but
exploration of the impact of different types of residential segregation on HPV vaccine uptake
has been limited.
140
Additionally, the relationship between uptake of COVID-19 vaccines and
HPV vaccination in sub-county geographies remains unexplored. It is important that we further
explore the contexts in which these factors impact HPV vaccine uptake to improve our
understanding of variation in HPV vaccination in small-area geographies within a large and
diverse urban center.
22
Methodologies to Elucidate Local Correlates of HPV Vaccination
More granular information on how these factors impact HPV vaccination at small area
geographies is necessary to identify differing vulnerabilities in local communities, and to design
interventions that appropriately address these factors. Geographic weighted regression (GWR)
allows for the modeling of spatial relationships that vary across a study area, while accounting
for spatial autocorrelation.
53,141
This is important, because the current data available to guide
local policymaking and resource allocation are based on the untested assumption that the same
factors impact HPV vaccine uptake equally across sub-county geographies, which may mask
variations in local, small-area patterns of vaccination behavior and uptake trends. Therefore, the
aim of Study 1 is to identify communities at high risk for cervical cancer and examine the
community-level factors associated with low HPV vaccination in communities across Los
Angeles County.
Based on the existing literature on community-based factors impacting HPV vaccination, we
hypothesize that zip code tabulation areas (ZCTA) with high proportions of residents living
below poverty, foreign-born, Latino, without insurance coverage, and residential segregation will
have lower ZCTA-level HPV vaccine initiation, compared to ZCTAs with lower proportion of
residents living below poverty, foreign-born, Latino, without insurance coverage, and residential
segregation (Hypothesis 1a).
Based on the literature examining the relationship between HPV-associated cancers and HPV
vaccination at state levels, which identified an inverse trend between HPV vaccination HPV-
associated cancer incidence and mortality,
100
we also hypothesize that there will be an inverse
relationship between cervical cancer incidence hotspots and HPV vaccination rates among
ZCTAS in LAC (Hypothesis 1b).
23
Lastly, acknowledging the impact of the COVID-19 pandemic on attitudes about vaccination
broadly, we also hypothesize that ZCTAs with low adolescent HPV vaccine uptake will also
have low adolescent COVID-19 vaccine uptake (Hypothesis 1c).
METHODS
Unit of Analysis & Eligibility Criteria
Study 1 incorporates cervical cancer incidence, HPV, TDAP, and COVID-19 vaccination, and
community-level sociodemographic and SDOH data. Our unit of analysis is the ZCTA.
ZCTAs are a geographic representation created by the U.S. Census Bureau of groups of
census blocks associated with different ZIP Codes.
142
ZIP Codes are used by the U.S. Postal
Service to deliver mail and constitute a part of all mailing addresses in the United States,
making them readily available for data collected from service delivery organizations which track
residential information about the populations they serve. While address information can be
associated with other geographic areas (census blocks, block groups, tracts, etc.), this requires
geocoding and other geographic estimation methods which can be resource and time intensive.
These other geographic areas are statistical subdivisions of a county created by the U.S.
Census to collect population data and are nested within county boundaries. ZCTAs do not align
perfectly with county boundaries and other U.S. Census defined geographies (blocks, block
groups, tracts).
143
Our analyses included all residential ZCTAs with land area within the Los Angeles County
boundary in which at least one cervical cancer case was diagnosed between 2006-2019.
However, tables and visualizations for geographies with results smaller than 11 cases have
been suppressed in line with data confidentiality standards.
24
Table 1. Study 1 Measures
DATA SOURCE VARIABLE
LEVEL OF
INFLUENCE
UNIT OF
ANALYSIS
Los Angeles
County Cancer
Surveillance
Program (2006-
2019)
Primary cancer site (cervix) Community ZCTA
Age-adjusted incidence Community ZCTA
Tumor behavior (malignant)
Community ZCTA
California
Immunization
Registry (2007-
2021)
Persons (age 9-17) with ≥1 dose HPV
vaccine
Community -
Outcome
ZCTA
Persons (age 9-17) with ≥1 dose
TDAP vaccine
Community ZCTA
2014-2019 5-year
American
Community
Survey
% Latino Community ZCTA
% <200% FPL Community ZCTA
% Non-US born Community ZCTA
% No health insurance coverage Community ZCTA
% Health insurance (private/public) Community ZCTA
Income concentration at the extremes
(calculated)
Community ZCTA
LACDPH COVID-
19 Vaccine
Dashboard
% (age 11-17) with ≥1 dose COVID-19
vaccine Community
LAC
Communities
Data Sources
HPV-Vaccination Data. We used state-reported count estimates of HPV vaccination uptake
from the State of California (California Immunization Registry, CAIR) as our outcome variable.
CAIR is a consolidated electronic statewide immunization registry responsible for storing and
managing immunization data for California residents; participation in CAIR is voluntary for
healthcare providers, pharmacies, schools, and childcare facilities
144
. Immunization providers
across the state upload data on immunizations administered after obtaining consent from
patients, parents or caregivers into an interactive platform which can produce comprehensive
immunization utilization reports and patient records. The registry is managed by the California
Department of Public Health. We received a limited data set from CAIR, which included:
Number of individuals aged 9-17 who have received at least one dose of HPV vaccine by zip
25
code ZCTA in Los Angeles County; individuals aged 9-17 who have received at least one dose
of TDAP vaccine by ZCTA in Los Angeles County.
Eligibility criteria: ZCTAs with at least 11 children aged 9-17 who received at least one dose of
either or both HPV and TDAP vaccine in a zip code within Los Angeles County from 2007-2021.
Uptake data on ZCTAs where less than 11 individuals were vaccinated during our study period
were unavailable (suppressed) due to CAIR confidentiality standards.
Cervical Cancer Incidence. Incidence of cervical cancer was examined using data from LA
SEER, which is the population-based Surveillance, Epidemiology, and Ends Results (SEER)
cancer registry for Los Angeles County. Variables included case counts by ZCTA for cases
identifying cervix as the primary cancer site. Our analysis included data from the time when the
HPV vaccine became available (2006) to the present (data most recently available is for 2019).
Eligibility Criteria: ZCTAs with at least 1 female diagnosed in Los Angeles County between
2006-2019 with cervical cancer as primary site (ICD-O-3 site recodes C53.0–C53.9) limited to
carcinomas (ICD-O-3 histology codes 8010–8671, 8940–8941), including cases at all stages
with malignant tumor behavior. ZCTAs with less than 11 cervical cases will be included in the
analyses but suppressed from resulting tables and maps (including cluster maps) to comply to
LA SEER confidentiality standards.
Area-level Sociodemographic Characteristics. We used census data at the ZCTA-level from
the 2014-2019 5-year American Community Survey (ACS). Variables used included ZCTA-level:
% Latino, % of population residing at <200% Federal Poverty Level, % of foreign-born
population, and % of population with no health insurance coverage. To assess residential
economic segregation, we used ACS variables to calculate ZCTA-level Income Concentration at
the Extremes (ICE)
145
: measure values range from -1 for communities with 100% of residents
from the most deprived economic group, to 1 for communities with 100% of residents from the
26
most privileged economic group. A value of 0 can indicate that either no residents in the ZCTA
are in an extreme income category, or that an equal number of ZCTA residents are in the two
extreme income categories.
Eligibility Criteria: ZCTA boundaries from the 2010 Census with land area within the Los
Angeles County boundary (2020 ZCTAs and ACS estimates were not used because 2020
Census population data is not yet available at the ZCTA-level).
COVID-19 Vaccination Data. Data from Los Angeles County Department of Public Health
(LCDPH) COVID-19 Vaccination Dashboard
146
on series initiation and completion for youth
ages 11-17 was used for 2020-2021. This data is available by LACDPH-defined Los Angeles
County communities.
Eligibility Criteria: Individuals ages 12-17 who had received at least one dose of the COVID-19
vaccine at a Los Angeles County community.
Analytic Approach
HPV vaccination rates were calculated using ZCTA-level population estimates from the 2010
Decennial Census for ages 9-17, and number of HPV vaccinated adolescents (ages 9-17) within
a ZCTA from CAIR. Since vaccination data was available for 15 years (2007-2021) and our
denominator consisted of a one-year population estimate, we divided our numerator by 15 to
calculate the yearly rate of HPV vaccine initiation. The yearly rate of HPV vaccine uptake was
multiplied by 100 for ease of interpretability. All analyses were performed using SAS (Version
9.4) and ArcGIS Pro (Version 3.0.3).
To test Hypothesis 1A, we performed ordinary least squares (OLS) linear regression analyses
including ZCTA-level percent poverty rate (continuous and categorical, in tertiles), percent of
foreign-born individuals (continuous and categorical, in tertiles), percent Latino ethnicity
27
(continuous and categorical, in tertiles), percent no insurance coverage (continuous and
categorical, in tertiles), TDAP utilization (continuous and categorical, in tertiles), and residential
segregation (categorical, in quintiles
145
) as predictors, and ZCTA-level HPV vaccination
(continuous) as the outcome variable (α=0.05). We used Pearson’s correlations and variance
inflation factors (VIF) to examine collinearity among predictors; correlations larger than 0.7 and
VIFs greater than 5 were considered problematic. This linear regression is a requisite first step
in identifying whether a relationship exists between HPV vaccine uptake and our hypothesized
predictors, but further examination is needed to elucidate whether these relationships are
accurately captured by the linear model or need spatial modeling techniques. A Moran’s I test of
the regression residuals was performed to test for spatial autocorrelation and assess whether
there was unexplained geographic variance in HPV vaccination which was not captured by the
multivariable OLS linear regression model. This step explores whether there is unexplained
spatial clustering which would imply that a global, non-spatial model (such as the OLS linear
regression) is insufficient to explain the associations between our predictors and outcome
variable. We performed a GWR to examine the relationship between area-level factors and HPV
vaccination across Los Angeles County ZCTAs; GWR assumes that there is spatial
autocorrelation in the data analyzed, and measures how the relationship between predictors
and the outcome variable varies across space.
141
For Hypothesis 1B, we first calculated a Moran’s I global statistic to identify geographic
clustering of cervical cancer cases at the ZCTA level in LA SEER data within Los Angeles
County and surrounding counties (Ventura, Kern, San Bernardino, and Orange). A Kernel
density function was then estimated to identify ZCTA-level incidence clusters (hot spots) of
cervical cancer across the study area. We performed a logistic regression using adolescent
HPV vaccination at the ZCTA-level as the predictor, and cervical cancer hot spot as a binary
outcome variable denoting whether a particular ZCTA was within a cervical cancer hot spot. We
28
used the coefficient of determination (R
2
) as a measure of how much of the variance in hot spot
distribution was explained by HPV vaccination, and hence how well HPV vaccination can
explain the distribution of cervical cancer hotspots in Los Angeles County. The regression
residuals were categorized into quartiles and a map of the residuals for each ZCTA in Los
Angeles County was created; this allowed us to better understand where and among whom
HPV vaccination is associated with cervical cancer hot spots. ZCTAs with a cervical cancer hot
spot and low HPV vaccination (i.e., an HPV vaccination rate below the Los Angeles County
mean) were considered at high risk for cervical cancer.
To investigate the relationship between HPV and COVID-19 vaccination uptake among
adolescents (Hypothesis 1C), we calculated a Pearson’s correlation coefficient between both
percentage of population vaccinated for ZCTA groupings in Los Angeles County, per LACDPH-
defined community boundaries. Given that the HPV vaccination data was available for ZCTAs
and the COVID-19 data was available for groups Los Angeles communities (groups of census
tracts), we used the Census Bureau relationship files to calculate the rates in equivalent areas
(ZCTAs).
Sensitivity Analysis
Kernel Density Analysis hot spot results are determined by arbitrary incidence cutoff points
which are not interpretable in themselves. It is therefore important to assess how sensitive the
underlying distribution of disease incidence is to the determination of disease hot spots based
on different cutoff points. We performed sensitivity analyses using different cervical cancer
incidence values as thresholds for establishing a hot spot and examined how different values
impacted the relationship with area level HPV vaccination rates. Our sensitivity analyses used
different threshold values within our Kernel Density Analysis to identify clusters which would
include both a high number of total cervical cancer cases (>40%) as well as a high density of
29
late-stage cases. Our definition of late-stage cancers included all regional, distant, and
unstaged cervical cancers at time of diagnosis; unstaged cases of cervical cancer were included
in the late-stage grouping due to their similar survival rate outcomes (see Figure 3). Our focus
was on total number of cases rather than on incidence rates because the purpose of our map is
to identify the areas of highest risk, and to later identify the most optimal locations at which to
implement strategies to improve HPV vaccine uptake (dissertation Study 3). In concordance
with LA SEER confidentiality standards, all areas containing less than 11 cases were excluded
from our final hot spots.
Figure 3. 5-year Survival Rates for Cervical Cancer in Los Angeles County by stage of diagnosis,
2012-2018 (California Cancer Registry)
30
To further provide context and usability to our analyses, we compared the geographies of
cervical cancer high risk with well-established boundaries for Los Angeles communities
147
. We
calculated the percentage of area included within the defined LA Times Neighborhood
boundaries (see Table 10 and Appendix 1). Our goal is to establish the best map of high
cervical cancer risk in Los Angeles County at small geographies, ensuring that our resulting
geographies have contextual meaning for local communities and can be actionable targets for
HPV vaccination campaigns and dissemination strategies.
RESULTS
There are 297 ZCTAs in Los Angeles; of these 15 corresponded to non-residential and
industrial areas (airports, theme parks, industrial zones, shopping centers, etc.) and were
removed from the analytic dataset. Of the remaining 282 ZCTAs, all had at least one case of
cervical cancer diagnosed between 2006-2019, and 5 (1.7%) were missing HPV uptake data
from CAIR. Given the small number of geographies with missing data, we performed a complete
case analysis; the remaining 277 ZCTAs corresponding to residential areas in Los Angeles
County with available CAIR data on HPV vaccine initiation constituted our analytic sample.
HPV vaccination uptake in Los Angeles County.
The ZCTA-level mean yearly HPV vaccine initiation in Los Angeles County during years 2007-
2021 was 5.1% (SD=1.8%). This range varied broadly, from 1% in the community of Westlake
Village in the Santa Monica Mountains to 16% in Downtown Los Angeles (Figure 4).
31
HYPOTHESIS 1 A
ZCTA-Level Predictors of HPV Vaccine Uptake
Table 2 shows the distribution of study predictors within Los Angeles County. Among ZCTAs in
Los Angeles County there are an average of 14% of households with incomes below the
Federal Poverty Level, with the smallest number of low-income residents in Manhattan Beach
Figure 4. Percent of yearly HPV vaccine initiation rate in Los Angeles County, 2007-2021
(California Immunization Registry)
32
(ZCTA 90266) and the highest concentration of low-income residents in Vernon (ZCTA 90058).
There is an average ZCTA-level Latino population of 41%, with the largest Latino population in
Maywood in Southeast Los Angeles (ZCTA 90270) and the smallest Latino population in Bel Air
(ZCTA 90077). The ZCTA-level mean of individuals not born in the United States is 32% with
the largest immigrant community in Glendale (ZCTA 91205) and the community with the
smallest percent of immigrants located in Acton (ZCTA 93510). ZCTA-level uninsurance
average in Los Angeles County is 8%; the LA area with most insured individuals in Westlake
(ZCTA 90057) and the area with the lowest percent of insured residents is Malibu (ZCTA
90263). The yearly average Tdap vaccine initiation rate was 6%, ranging from less than 1%
(0.10%) in Thousand Oaks (ZCTA 91362) to 19% in Downtown Los Angeles (ZCTA 90014).
ZCTA-level average of population of individuals ages 9-18 (our study population) in Los Angeles
County was 13%, with the community of Northridge (ZCTA 91330) having the highest percent of
young individuals, while Downtown Los Angeles had the lowest percent of young individuals
(ZCTA 90014). The areas in Los Angeles County with the most income segregation were Bel
Air (ZCTA 90077) and Vernon (ZCTA 900058), with the largest percent of privileged and
disadvantaged residents, respectively.
Table 2. Demographic characteristics of ZCTAs in Los Angeles County
Mean (SD) Minimum Maximum
% Below FPL
% Latino Ethnicity
% Non-US Born
% Uninsured
Income Concentration at the Extremes
Quintile 1 (<-0.11, most disadvantaged)
Quintile 2 (-0.11 – 0.02)
Quintile 3 (0.02 – 0.13)
Quintie 4 (0.13 – 0.28)
Quintile 5 (> 0.28, most privileged)
% Population Ages 9-18
% Yearly Tdap Vaccine Initiation Rate
13.77 (7.90)
40.93 (25.78)
31.93 (12.01)
8.47 (4.74)
0.08 (0.21)
13.30 (4.10)
6.06 (2.06)
3.24
3.75
7.64
0.60
-0.47
1.32
0.10
49.37
98.35
63.95
29.95
0.64
26.25
18.78
33
Bivariate Linear Regressions
Linear regression models were estimated for each of the proposed predictors and percent of
yearly HPV vaccine initiation as our first step in model building; all were found to be significantly
and positively associated with HPV vaccine uptake (Table 3). All models tested met the
assumptions of linear regression.
Table 3. Linear regression model results of percent of HPV vaccine initiation.
Predictor Coefficient 95% CI P-value
% Yearly Tdap Rate 0.852 0.825 - 0.879 <0.001
T1 (Lowest % Tdap Rate)
T2
T3 (Highest % Tdap Rate)
-0.034
-0.0.17
(Reference)
-0.037 – -0.30
-0.021 – -0.014
-
<0.001
<0.001
-
% Latino 0.030 0.023 - 0.038 <0.001
T1 (Lowest % Latino)
T2
T3 (Highest % Latino)
-1.779
-0.955
(Reference)
-2.262 – -1.295
-1.438 – -0.473
-
<0.001
<0.001
-
% Non-US Born 0.030 0.012, 0.047 0.001
T1 (Lowest % Non-US Born)
T2
T3 (Highest % Non-US Born)
-0.917
-0.294
(Reference)
-1.433 – -0.400
-0.809 – -0.221
-
<0.001
0.262
-
% Uninsured 0.203 0.164, 0.241 <0.001
T1 (Lowest % Uninsured)
T2
T3 (Highest % Uninsured)
-2.244
-1.542
(Reference)
-2.696 – -1.790
-1.993 – -1.091
-
<0.001
<0.001
-
% Below FPL 0.154 0.13, 0.174 <0.001
T1 (Lowest % Below FPL)
T2
T3 (Highest % Below FPL)
-2.448
-1.369
(Reference)
-2.878 – -2.018
-1.788 – -0.940
-
<0.001
<0.001
-
ICE Quintiles
Q1 (Most disadvantaged)
Q2
Q3
Q4
Q5 (Most privileged)
3.091
1.650
1.223
0.596
(Reference)
2.941 – 3.587
1.102 – 2.198
0.675 – 1.772
0.048 – 1.438
-
<0.001
<0.001
<0.001
0.033
-
We explored the correlation between our predictor variables as the next step before creating a
multivariable model (see Table 4). While both measures of poverty and residential segregation
were significantly associated with HPV vaccine uptake in the bivariate analyses, both could not
be included in the same multivariable model due to their high structural correlation (Pearson
Correlation=0.88). Residential segregation is calculated in part by subtracting the number of
34
individuals in the least privileged income group from those in the most privileged income group
(per Krieger et al, the 20
th
and 80
th
income percentiles). Based on 2017 income estimates,
148
individuals residing below the FPL would be included as part of the ICE calculation and would
hence appear twice in the model.
Table 4. Pearson Correlation Coefficients.
% Latino % Foreign-
Born
% No
Insurance
% Below
FPL
ICE
TDAP Rate 0.28 0.17 0.42 0.64 -0.54
% Latino 0.33 0.72 0.53 -0.67
% Foreign-Born 0.57 0.37 -0.48
% No Insurance 0.72 -0.80
% Below FPL -0.88
To examine whether the significant statistical association between residential segregation and
HPV vaccine uptake was a result of the inclusion of the high- and low-income categories
independently, or due to the effect of the high- and low-income categories in combination (i.e.,
residential segregation), we explored the interaction between high- and low-income categories.
We found that while both income extremes were associated with HPV vaccine uptake, their
interaction was not itself significantly associated with our outcome variable (p=0.125); we
therefore excluded residential segregation from our multivariable model. To ameliorate the
impact of the elevated correlations among the remaining variables, we used measures of Latino
ethnicity and uninsurance which were mean centered for the remaining analyses.
Multivariable Models
We explored the impact of our statistically significant predictor variables on yearly HPV
vaccination rate through a linear multivariable regression model (Model 1, Table 5). We found
that after controlling for all other predictors, a one per hundred increase in ZCTA-level yearly
Tdap initiation rate was associated with a 0.8 mean increase per hundred in yearly HPV vaccine
35
initiation rate (p<0.01); that a 10% increase in the ZCTA-level Latino population was associated
with a 0.09 increase per hundred in the average rate of yearly HPV vaccine initiation (p<0.01);
and that a 10% increase in ZCTA-level uninsured population was associated with a 0.35
increase per hundred in yearly HPV vaccine initiation rate, on average (p<0.01). In our
multivariable model, the direction of the relationship between percent of non-US born population
changed, such that a 10% increase in the non-US born population at the ZCTA-level was
associated with a 0.07 decrease per hundred in average yearly HPV vaccine initiation (p<0.01).
The association between percent of the population residing below the poverty level and HPV
vaccination lost statistical significance (p=0.45) in the multivariable model. No VIFs above 5
were observed for any predictor.
Table 5. Multilinear regression model (Model 1: Adjusted R
2
=0.960, AIC=220.78)
Variable Coefficient P-Value VIF 95% CI
Intercept 0.506 <0.001 0 0.272 – 0.740
TDAP Rate 0.799 <0.001 1.7 0.771 – 0.827
% Latino 0.009 <0.001 2.1 0.007 – 0.012
% Non-US Born -0.007 0.001 1.5 -0.012 – -0.003
% Below FPL -0.004 0.453 3.0 -0.013 – 0.006
% Uninsurance 0.035 <0.001 4.0 0.017 – 0.052
We tested these associations using categorical versions of all predictors (Model 1a, Table 6).
We continue to see a linear and positive relationship between average yearly HPV vaccination
rate per hundred and ZCTA-level percent Tdap uptake and ZCTA-level percent uninsurance, so
that ZCTAs within the lowest tercile for both Tdap utilization and uninsurance rates have lower
HPV vaccine uptake per hundred compared to the ZCTAs with the highest Tdap vaccination
and percent uninsurance (-0.28, p<0.01, and -0.34, p=0.04, respectively). The relationship
between ZCTA level HPV vaccine uptake and percent of the population in poverty remained
statistically insignificant in this model.
36
We observed changes in the relationship between HPV vaccination and ZCTA-level percent
Latino and Non-US born populations from our original model (Model 1). We see that both
relationships loose statistical significance in this multivariable model, and that the ZCTAs with
scores in the lowest tercile for percent Latino and Non-US born populations are associated with
higher increases in HPV vaccination than those in the middle tercile in both cases. We believe
this is due to the influence of outlier observations with high HPV vaccination rates in the lower
tercile for both predictors (see Figure 5 for the scatterplots of ZCTA-level percent Latino and
percent non-US born populations and percent HPV vaccination rates). These outliers highlight
the importance of modeling different geographies separately, further supporting our use of local
geographic estimation models (GWR). The explanatory value of the multivariable model was
reduced using categorical versions of our predictors when compared to our model using linear
versions (R
2
=0.59 vs R
2
=0.96), so we continued our model building using continuous versions
of our predictors, as in Model 1.
Table 6. Multilinear regression model using predictors categorized as tertiles. (Model 1b:
Adjusted R
2
=0.588)
Predictor Coefficient P-value
VIF
95% CI
Intercept 7.028 <0.001
0
6.712 – 7.343
% Tdap Rate
Q1 (Lowest % Tdap Rate)
Q2 (Median)
Q3 (Highest % Tdap Rate)
-0.283
-0.015
(Reference)
<0.001
<0.001
-
1.7
-0.033 – -0.024
-0.019 – -0.011
-
% Latino
Q1 (Lowest % Latino)
Q2 (Median)
Q3 (Highest % Latino)
0.177
0.131
(Reference)
0.463
0.498
-
2.0
-0.270 – 0.650
-0.250 – 0.512
-
% Non-US Born
Q1 (Lowest % Non-US Born)
Q2 (Median)
Q3 (Highest % Non-US Born)
0.188
0.063
(Reference)
0.367
0.720
-
3.4
-0.221 – 0.596
-0.282 – 0.408
-
% Below FPL
Q1 (Lowest % Below FPL)
Q2 (Median)
Q3 (Highest % Below FPL)
-0.420
-0.197
(Reference)
0.136
0.377
-
1.7
-0.974 – 0.133
-0.635 – 0.241
-
37
% Uninsured
Q1 (Lowest % Uninsured)
Q2 (Median)
Q3 (Highest % Uninsured)
-0.637
-0.662
(Reference)
0.047
0.005
-
1.9
-1.266 – -0.009
-1.125 – -0.199
-
We tested the robustness of our linear model (Model 1) by substituting a measure of ZCTA-level
public insurance (instead of uninsurance) and found that the magnitude and direction of the
model predictions remained unchanged, but the correlations among predictors (as determined
Figure 5. Scatterplots of ZCTA-level HPV Vaccination Rate with Percent Latino (Box A) and
Percent Non-US Born (Box B).
A
B
38
by the VIFs) and the overall explanatory value of the model (per the R
2
) worsened with this
change (Table 7).
Table 7. Multilinear regression model replacing Uninsurance with Public Insurance measure.
(Model 2: Adjusted R
2
=0.958)
Variable Coefficient P-Value VIF 95% CI
Intercept 0.390 0.001 0 0.160 – 0.620
% Tdap Rate 0.793 <0.001 1.9 0.763 – 0.822
% Latino 0.013 <0.001 2.1 0.011 – 0.015
% Non-US Born -0.002 0.264 1.3 -0.007 – 0.002
% Below FPL 0.010 0.080 3.8 -0.001 – 0.020
% Public Insurance -0.006 0.138 4.1 -0.014 – 0.002
We evaluated a model that included only variables significantly associated with yearly rate of
HPV vaccine initiation (i.e., removed the measure of poverty), and found a higher R
2
and lower
AIC compared to our original model; we selected this abbreviated model as our final model for
all further analyses.
Table 8. Multivariable linear regression model only including variables with significant
associations (Final Model: Adjusted R
2
=0.962; AIC=220.42)
Variable Coefficient P-Value VIF 95% CI
GWR Range
Intercept 0.516 <0.001 0.0 0.306 – 0.725 -
% Tdap Rate 0.796 <0.001 1.2 0.773 – 0.818 0.65 – 0.98
% Latino 0.009 <0.001 2.1 0.007 – 0.012 -0.008 – 0.030
% Non-US Born -0.007 0.002 1.5 -0.011 – -0.003 -0.041 – 0.045
% No Insurance 0.031 <0.001 3.2 0.015 – 0.047 -0.147 – 0.086
After calculating the Moran’s I global statistic, we found that there was significant clustering in
the residuals of our final model (Moran’s Index=0.048, p<0.01), justifying the use of geographic
weighted regression.
39
Geographic Weighted Regressions
The results of our GWR identified non-stationarity (geographic variation in relationships) in all
predictors explored (Table 8). While the multivariable linear regression model coefficient for
yearly Tdap initiation rate was 0.80, after controlling for all other variables in the model the GWR
coefficients ranged between 0.65 and 0.98, with the lowest and highest associations in Azusa
(ZCTA 91702) and Carson (ZCTA 90746), respectively (Figure 6). The OLS model regression
coefficient for percent Latino population was 0.009, and the GWR coefficients varied broadly,
from -0.008 in South Los Angeles (ZCTA 90074) to 0.030 in Tujunga (ZCTA 91042, Figure 7).
Similarly, local coefficient ranges for ZCTA-level percent uninsured populations (Figure 8) and
non-US born populations (Figure 9) extended into the opposite direction than the linear model
estimates, meaning that the relationship was positive in some communities and negative in
others. The GWR coefficients for the association between uninsured populations and mean
yearly rate of HPV vaccine initiation per hundred ranged between -0.15 in Palmdale (ZCTA
93550) and 0.09 in Glassell Park (ZCTA 90065), while the coefficient in the OLS model was
0.03; and the GWR coefficients for ZCTA non-US born populations ranged from -0.04 in
Westchester (ZCTA 90045) to 0.045 in Catalina Island (ZCTA 90704) while the OLS coefficient
was -0.007. Figures 7, 8, and 9 highlight the areas in which the association was positive (in
green), and those in which it was negative (in purple).
Model fit statistics improved in the GWR model, with an increased adjusted R
2
=0.98 and a lower
AIC=63.1 Table 9 summarizes the model fit statistics in the exploratory OLS (Model 1), final
OLS, and GWR models.
Table 9. Model diagnostics for OLS and GWR.
Exploratory OLS Final OLS GWR
Adjusted R2 0.960 0.962 0.983
AIC 220.78 220.42 63.10
40
Figure 6. GWR Regression Coefficients for percent yearly Tdap initiation rate.
41
Figure 7. GWR Regression Coefficients for percent of Latino population.
42
Figure 8. GWR Regression Coefficients for percent uninsured population.
43
HYPOTHESIS 1 B
Areas at High Risk for Cervical Cancer
We defined ZCTAs as being at high risk for cervical cancer if they were located within a cervical
cancer hot spot and had low rates of HPV vaccine initiation (lower than the mean rate of HPV
Figure 9. GWR Regression Coefficients for percent non-US born population.
44
vaccine initiation). Figure 10 shows the number of hot spots, percent of total cases and late-
stage cases, and proportion of total Los Angeles County late-stage cases included in the
clusters based on different cluster thresholds. We selected 110 as the threshold value for our
cervical cancer clusters as it included the largest proportion of late-stage cases in Los Angeles
County as well as more than 40% of all cases of cervical cancer in our study area. Figure 11
shows the location of the cervical cancer clusters as well as all ZCTAs in Los Angeles County
which overlap with a cervical cancer cluster (N=197).
Figure 10. Threshold values for cervical cancer clusters.
45
Logistic Regression
We found that HPV vaccine initiation per hundred explained 13% of the deviance in cervical
cancer clusters in Los Angeles County (OR=1.90, p<0.01). A map of the regression residuals
shows that the prediction model best explained cervical cancer clusters in Central, South and
Figure 11. ZCTAs in LAC overlapping a cervical cancer cluster.
46
Southeast Los Angeles, in the communities surrounding the San Pedro Harbor, and in the
central and northern Antelope Valley (see Figure 12).
Figure 12. Map of regression residuals of the relationship between HPV vaccine uptake and
cervical cancer clusters.
47
Communities at High Risk of Cervical Cancer
After identifying ZCTAs within the cervical cancer clusters which contained HPV vaccine
initiation rates below the area County average, we found that 76 ZCTAs in Los Angeles County
(27%) were at high risk for cervical cancer (see Figure 13). While it is beyond the scope of this
dissertation to provide a detailed characterization of the communities aligned with areas at high
risk of cervical cancer in Los Angeles County, it is noteworthy that almost one third of ZCTAs in
our analytic sample are included in this definition. Affected areas comprise communities with
diverse sociodemographic characteristics, including densely populated areas within West Los
Angeles, Southeast Los Angeles, and Long Beach; some suburban communities in the San
Gabriel, Pomona and San Fernando Valleys; and some rural areas in the Angeles Forest.
48
Los Angeles County Neighborhoods at High Risk of Cervical Cancer
108 out of 272 (40%) Los Angeles County neighborhoods (as defined by the LA Times Mapping
Project) contained at least 1% of land area corresponding to high risk ZCTAs, identified above.
Figure 13. LAC ZCTAs at high risk for cervical cancer.
49
Appendix 1 has a full list of affected neighborhoods, and the percent of the neighborhood
overlapping with a high-risk area. Table 10 below lists the most vulnerable neighborhoods,
defined as those with over 75% overlap with areas of cervical cancer high risk.
Table 10. Los Angeles neighborhoods at high risk of cervical cancer.
Los Angeles Neighborhood % Overlap
Torrance 76.13
Industry 78.04
Irwindale 78.79
Eagle Rock 84.06
Toluca Lake 84.20
West Hollywood 84.29
Westwood 84.95
Claremont 85.02
Brentwood 85.85
Valley Village 85.94
Tarzana 89.54
Altadena 89.84
Whittier Narrows 90.65
Tujunga 93.49
Cheviot Hills 94.96
San Pedro 96.06
Rowland Heights 96.69
Westchester 96.87
Rolling Hills 97.06
Rolling Hills Estates 97.51
Hawaiian Gardens 97.64
Cerritos 97.77
Walnut 98.12
Rosemead 98.53
Lomita 99.11
Sunland 99.12
Hollywood Hills 99.18
Lakewood 99.19
Manhattan Beach 99.24
South El Monte 99.39
West Covina 99.45
Fairfax 99.49
Monterey Park 99.58
Hollywood Hills West 99.76
Palos Verdes Estates 99.81
San Gabriel 99.88
50
Alhambra 99.88
Griffith Park 99.91
South San Gabriel 99.93
Atwater Village 99.93
Los Feliz 99.93
East San Gabriel 99.93
San Pasqual 99.95
El Monte 99.97
South San Jose Hills 100.00
Pico-Robertson 100.00
Temple City 100.00
Rancho Park 100.00
Arcadia 100.00
Baldwin Park 100.00
La Puente 100.00
Valinda 100.00
East Pasadena 100.00
West Puente Valley 100.00
North El Monte 100.00
DISCUSSION
Our study aimed to identify spatial patterns in HPV vaccination in Los Angeles County; to
understand the factors impacting HPV vaccination across Los Angeles County communities;
and to characterize the neighborhoods in the County at high risk of cervical cancer.
HPV Vaccine Uptake
Our results show rates of adolescent HPV vaccine initiation in Los Angeles County well below
national averages for that same time period (2007-2021) based on NIS-Teen data reports
41
(57.6%) as well as Los Angeles County uptake estimates based on parental self-reported data
(LACHS
149
in 2018, 47.2%). We also found that the yearly rate of HPV vaccine uptake varied
greatly in ZCTAs within Los Angeles County; to our knowledge, this is the first study to depict
the distribution of HPV vaccination in such geographic detail using population-based
immunization registry information (from CAIR).
51
OLS Regression Results
Our global (OLS) models found that on average, ZCTAs with higher non-US born populations
had lower mean yearly HPV vaccine initiation rates, as we hypothesized (Hypothesis 1a).
Additionally, these global models found that ZCTA-level poverty was not significantly associated
with HPV vaccine uptake after adjusting for the other predictors in our model: other studies had
found both positive and negative associations between HPV vaccination and area level
poverty.
37,53,137-139
However, contrary to what we hypothesized (Hypothesis 1a), we found that ZCTAs with higher
percent of Latino and uninsured populations had higher HPV vaccine initiation rates. While
previous studies had reported mixed associations between HPV vaccination and Latino ethnicity
based on other area characteristics,
140
our findings align with those of Henry and colleagues,
who found that Latina girls residing in predominantly Latino neighborhoods had higher rates of
HPV vaccine initiation than Latina girls residing in communities with smaller Latino
populations.
140
It is possible that these improved vaccination rates could be a consequence of
residing in communities with high social capital and shared health-related values,
134
including
positive attitudes surrounding vaccination.
8,73,74
Uninsurance has been previously found to be associated with lower HPV vaccine uptake,
53
in
line with our study results. Some authors have posited that the relationship between higher HPV
vaccine uptake in low-income communities is the result of the greater availability in these
communities of safety-net clinics and federal programs providing free HPV vaccinations like the
Vaccines for Children Program,
65,66,140
which could explain why our measure of ZCTA-level
poverty lost statistical significance once we adjusted for uninsurance in our models. Additionally,
increases in HPV vaccine uptake have been observed among states which were part of the
Affordable Care Act Medicaid expansion
150-153
as is the case for California, which increased
52
healthcare access for uninsured populations. These results could provide support for
interventions focused on optimizing HPV vaccine uptake at safety-net clinics.
While we were unable to include residential segregation in our multivariable model due to
structural collinearity issues, our bivariate analysis found that the areas with most extreme
segregation of low-income residents were associated with the highest yearly rates of HPV
vaccine initiation, compared to the areas with most extreme segregation of high-income
residents. This suggests that residential segregation may not be a driving factor in low HPV
vaccination uptake; in fact, among low-income communities, residential segregation seems to
operate as a protective factor, reducing risk of HPV associated burden. As such, these
communities provide an opportunity to better understand the neighborhood characteristics that
may contribute to such a protective effect. Further research should focus on gathering a more
comprehensive view of such factors in these communities to identify modifiable factors which
could help us design interventions which can attempt to replicate these characteristics in low-
uptake, high-risk communities. Our findings also imply that residing in homogeneous
communities, at least in terms of income, can impact attitudes and behaviors surrounding HPV
vaccine uptake. Area-based influences including social information networks, cultural values,
and behavioral norms surrounding HPV vaccination and vaccine acceptability could play a role
in the relationship we observed. Previous research has observed negative attitudes towards
childhood immunizations among residents of segregated high-income communities.
140,154
Such
social norms can impact HPV vaccination intentions and behavior,
155-157
as postulated by the
normative belief construct of the Theory of Planned Behavior.
158,159
This is an important contribution to the literature because our study is, to our knowledge, the
first to incorporate a measure of economic residential segregation to the study of area-level
HPV vaccinate uptake. While Henry and colleagues explored the impact of racial segregation
53
and low-income communities on HPV vaccine uptake, they did not explore HPV vaccination
uptake and residential income segregation (communities where low income or high income
individuals reside, exclusive of each other).
140
Results of Geographic Weighted Regression
Furthermore, our analyses uncovered differences between the results of OLS regression and
GWR in explaining the relationship between predictors and HPV vaccine uptake. Notably, local
coefficient ranges for ZCTA-level percent Latino, uninsured populations and non-US born
populations extended into the opposite direction than the global linear model estimates,
meaning that we found HPV vaccine initiation to be positively associated with larger Latino,
uninsured and non-US born populations in some ZCTAs of Los Angeles County, while being
negatively associated with them in other areas. We need to understand the factors driving these
different associations with HPV vaccination further, as they could necessitate far different
intervention strategies. For example, in Latino communities with high rates of misinformation
about the HPV vaccine, culturally relevant educational strategies (e.g., radionovelas, use of
promotores de salud) could improve knowledge about the HPV vaccine.
160,161
On the other
hand, among communities with high medical mistrust trust-building with community partnerships
could be a preferred strategy, as was used to support COVID-19 vaccination campaigns.
162
The association between higher HPV vaccine uptake among some communities with larger
uninsured, Latino, and non-US born populations could be a consequence of the clustering of
safety-net clinics in some communities, especially in South and Downtown Los Angeles among
Latino and other immigrant communities;
102
previous research has identified greater healthcare
utilization among those residing closer to safety-net healthcare providers.
163
Tsui and
colleagues identified the shortest travel distance and public transportation times to safety-net
clinics among Latinas in Los Angeles; while they found no association between HPV uptake and
54
proximity to safety-net clinics after controlling for individual-level factors, this could have been in
part a result of their focus on immigrant, low-income women.
While coefficients for percent Latino population and HPV vaccine uptake were small across Los
Angeles County, GWR results underscore how the relationship between Latino populations and
HPV vaccine uptake can be negative in some communities and positive in others, even after
adjusting for common confounders such as insurance coverage and nativity. The varying
relationships and diverse demographic profiles of these communities emphasizes the diversity
in health beliefs and behaviors related to HPV vaccine uptake among Latino subgroups,
8,44-46
suggesting different local patterns of individual-level factors such as vaccine hesitancy, medical
mistrust, or exposure to misinformation about the HPV vaccine, which would necessitate
different intervention strategies and approaches. The importance of these differences has been
previously identified for other kinds of cancer screening and risk behaviors within Latino
subgroups, including Pap Smear testing trends, mammography and colonoscopy uptake, and
tobacco use.
164-169
For example, we observed a negative association between HPV vaccine uptake and both Latino
ethnicity and non-US born populations among some Los Angeles communities with large Latino
immigrant populations, such as South Los Angeles.
147
Mistrust and vaccine hesitancy have
been identified as a barriers to vaccination among Latino immigrant communities.
43,170
In
addition to misinformation and fears about vaccine harms, language barriers and fear of
immigration authorities have been reported as barriers to vaccination uptake in this
community.
170
Leveraging trusted sources of information among this group offer opportunities to
provide accurate vaccine messaging, such as by using Spanish-language news outlets for
vaccine education and referral campaigns, since use of these have been associated with
55
increased trust in journalists and health officials.
171
Similarly, successful COVID-19 vaccination
campaigns have relied on community partnerships to cultivate trust and on removing access
barriers by providing multiple vaccination avenues, provided at consistent times and
locations.
162
The use of community health workers/promotores de salud has also been
successfully implemented to increase awareness and uptake of HPV vaccination.
161
The use of
culturally concordant clinical sites with language concordant providers and outreach workers
have also been identified as facilitators of vaccine uptake among undocumented parents in
Northern California.
172
Rosenstock’s Health Belief Model
173
supports the use of such interventions. Vaccination
education campaigns can help individuals understand the perceived benefits of the HPV
vaccine among their children, and the use of language-concordant services and referrals can
reduce perceived barriers. Community health workers/promotores de salud can provide cues to
action that nudge parents to seek vaccination services for their children. Lastly, the tailoring of
education messaging and intervention content to specific communities, especially when
developed with community input, can drive the overall health beliefs surrounding HPV
vaccination which can drive vaccine uptake.
174,175
The strongest association we identified was between area-level HPV and Tdap vaccine uptake.
While the strength of the relationship varied across Los Angeles County, it was always positive
and larger than those of any other predictor considered in our model. Interventions that aim to
improve the co-administration of Tdap and HPV vaccination should be prioritized as they could
serve as an effective strategy for improving population-level HPV vaccination among all Los
Angeles County communities.
110,115,176,177
Our results provide a blueprint for identifying the
communities which would most benefit from implementing such interventions.
56
Our results suggest that OLS models may mask the spatial patterns present in the relationship
between area-based factors and HPV vaccine uptake among Los Angeles County communities.
This is a property of models that use averages to estimate the relationship between multiple
factors, and it underlines the importance of understanding the limitations of such models in
providing an accurate picture of the distribution of the observations that underlie such averages.
In the case of geospatial models, it points to the importance of examining the residuals of such
models to identify any unexplained spatial autocorrelation to ensure the use of models that
appropriately account for any spatial relationship which may be at play. This highlights the need
to use local estimation methods to fully understand the range of associations present in these
relationships and the impact that spatial correlation has on these associations.
The results of our GWR models identified noteworthy variation in the patterns of HPV vaccine
uptake and relationships with correlates of HPV vaccination across Los Angeles County, yet the
area-level, publicly available data used in this study cannot fully explain the variation observed.
In order to interpret such results in full, more targeted data collection efforts are needed in the
identified communities, including the collection of rich qualitative data from a variety of HPV
vaccine stakeholders; data on healthcare availability and utilization; and survey data which can
assess knowledge, attitudes, and beliefs regarding adolescent HPV vaccination among parents
of adolescents residing in such communities. By identifying the specific patterns present across
the County, our results highlight areas in which such efforts can be focused.
Cervical Cancer Incidence and HPV Vaccination
Contrary to our second hypothesis (Hypothesis 1b) we found a positive relationship between
cervical cancer incidence hotspots and yearly rate of HPV vaccine initiation, suggesting that
57
areas with higher HPV vaccine initiation are also burdened with high cervical cancer incidence.
Vickers and colleagues uncovered a similar trend in Alabama, and postulated that there could
be an association between perceived cancer susceptibility and HPV uptake behavior in those
communities.
178
The relationship we observed could perhaps also be explained by the lag
between exposure to HPV infection and the onset of cervical cancer, and the successful
targeting of HPV vaccination campaigns to communities most vulnerable to cervical cancer in
Los Angeles County. It is possible that while HPV vaccine initiation is high in these
communities, it is yet too early to see the corresponding reductions in population-level cervical
cancer incidence associated with lower HPV infection rates. Alternatively, while our study
examined HPV vaccine initiation, it is also possible that rates of HPV vaccine completion are
low in these areas, reducing the potential protective effect of the HPV vaccine in preventing
cervical cancer. While official immunization estimates of vaccine completion for Los Angeles
County ZCTAs were not available to us at the time of the study, national vaccination estimates
(per NIS-Teen
41
) and previous literature have noted that rates of HPV vaccine series completion
lag behind series initiation
53,179
, especially among communities of color and Latinos
37,53,180
which are disproportionately impacted by cervical cancer.
5,181
COVID-19 and HPV Vaccination Uptake
We were unable to explore the relationship between ZCTA-level uptake of COVID-19 and HPV
vaccines among youth in Los Angeles County due to changes in County level data reporting for
COVID-19 vaccination among youth.
146
Instead of providing youth uptake data for census tracts
and Los Angeles communities, the data is now available only for Los Angeles communities,
which have a many to many relationship with census tracts. This change made it impossible for
us to calculate comparable estimates between COVID-19 vaccination for this age group and
HPV vaccine uptake using CAIR data, which is available at the ZCTA level. Changes in COVID-
58
19 data availability have been noted elsewhere and identified as a result of health departments
adapting to the progression of the COVID-19 pandemic nationwide.
182
Strengths and Limitations
Our study contributes to the literature by being the first (to our knowledge) to use official
estimates of HPV vaccine uptake (from CAIR) to explore sub-county HPV vaccine initiation, and
to explore the factors associated with uptake of HPV vaccination in Los Angeles County at
geographies smaller than the county (ZCTAs). Our study also contributes to the literature on the
impact of residential segregation on health outcomes by being exploring the association
between economic residential segregation and HPV vaccine uptake. Another strength of our
research is its use of cancer registry (LA SEER) and immunization registry (CAIR) data in
tandem to identify the areas in Los Angeles County at high risk for cervical cancer; and by then
identifying how cervical cancer high-risk areas overlap with known LA community boundaries,
providing important context and improving the usability of the patterns found. This can have
important implications for service delivery and resource distribution in Los Angeles County.
A limitation of our research is the dynamic nature of populations; individuals may not live in the
same place for long period of times, and disease estimates based on delayed data may not
accurately reflect the health behaviors or disease distribution of the underlying population. It is
possible we are comparing health behaviors (HPV vaccine uptake) and health outcomes
(cervical cancer incidence) among populations that are constitutionally different. However, for
the purposes of this study we assumed that population dynamics were not systematic in terms
of cancer incidence and vaccination status and that these changes will not alter the distribution
of cervical cancer risk. Study results are also limited to populations living in urban centers with
large Latino populations; the relationships we observed may be affected by positive or negative
health effects of residing in an ethnic enclave,
183-185
as have been observed for other health
59
outcomes.
186-190
Further research should examine these associations in more racially/ethnically
homogeneous communities.
A common limitation of all studies incorporating geospatial analyses is the modifiable areal unit
problem (MAUP), which notes that different relationships can emerge in spatial data depending
on the boundaries used. It is possible that the relationships we found may be different using
different small area geographic boundaries, as arbitrary summary geographies can
misrepresent the true location of populations and their exposures.
Additionally, the quality of the data collected by CAIR may have impacted our results. Not all
healthcare providers were mandated to report vaccinations to CAIR prior to 2023, so it is likely
that not all of the vaccines administered in California were captured in the registry. Given that
the rates we observed are well below other national and local estimates,
41,146
it is possible that
CAIR reports undercount the real number of adolescent HPV vaccinations in Los Angeles
County, especially during the earlier years of our data range (2007-2021) when electronic health
record technologies were first being implemented by healthcare systems across the country.
Furthermore, providers in limited resource settings may have less time and staff resources
available to meet CAIR reporting requirements, so this undercount may disproportionately
impact providers offering low-cost or free vaccination services, which could have biased some
of the relationships we observed. In addition, the disruptions caused by the COVID-19
pandemic could have resulted in lower rates of HPV vaccine uptake during years 2020-2021.
Another limitation of our study was that we did not have perfect alignment in the time periods
and populations for which the data was available due to our use of multiple data sources (LA
SEER, CAIR, ACS, Decennial Census). Furthermore, CAIR data was available for a broader
age of adolescents (ages 9-17) than those for whom the HPV vaccine is routinely recommended
60
(ages 11-13), making it possible that our analyses incorrectly compared different groups of
individuals, and that factors excluded from our analyses could be impacting or confounding our
results.
Our cervical cancer clusters excluded geographies with values below 11 due to cancer registry
confidentiality standards, which may have impacted the definition of our cervical cancer clusters.
However, our focus was on identifying areas at high risk for cervical cancer at a population
level, so that geographies excluded from our analyses would not have been the most impactful
due to their small absolute number of cases.
Nonetheless, we believe our results constitute an important first step in exploring the factors
impacting HPV vaccine uptake at sub-county geographies in Los Angeles County with the data
that is currently available which had been absent from the literature. Future research should
compare our results with analytic results using other geographic boundaries (especially census
tracts) once HPV uptake estimates become available for those areas.
Our results are applicable to area-level relationships only and are not meant to explain
individual HPV vaccination behavior (the ecological fallacy); our study results cannot speak to
whether Latino, non-US born or uninsured individuals, or individuals who have received the
Tdap vaccine are more or less likely to have received the HPV vaccine. While the relationships
identified through our research can act as starting points for the formulation of hypotheses on
these relationships, they would have to be tested in studies designed using individual level
measures.
Lastly, care should be placed in the interpretation of maps in where the unit of analysis varies in
sizes. Some ZCTAs in Los Angeles County in more rural areas extend over large areas, while
61
ZCTAs in more densely populated areas are smaller, yet each of these constitute units of equal
value in our analyses and results.
Study Implications
Identifying variation in sub-county factors associated with HPV vaccine uptake can help us
identify where to deliver which interventions for the greatest population-level improvements in
cervical cancer burden. This is especially impactful for urban centers like Los Angeles County,
where diverse communities with different language and cultural needs coexist. The results from
this study can provide guidance not only on the relationships between community-level factors
and HPV vaccine uptake, but about how these relationships vary over space. This can provide
an outline of the communities most at risk requiring prioritization in planning decisions, but also
on the type of interventions that need to be developed to address the community-level factors
impacting HPV vaccination specific to each community. Such targeted interventions hold
promise for improving population-level HPV vaccine uptake among the most vulnerable
communities.
62
CHAPTER 4: Study 2: Individual and Interpersonal Factors Driving Adolescent HPV Vaccine
Uptake among Latinos in a High-Risk Community for Cervical Cancer
ABSTRACT
Background: Latino communities are disproportionately impacted by some HPV associated
cancers, yet our understanding of the factors impacting adolescent HPV vaccination in Latino
communities at high risk of cervical cancer is scant. We also know little about whether Latinos of
different acculturation levels residing in these high-risk communities are differently impacted by
these factors. Our aim was to identify factors impacting adolescent HPV vaccination in high and
low acculturated Latino parents in a community at high risk for cervical cancer.
Methods: Surveys examining HPV vaccine hesitancy in an urban community with low HPV
vaccine uptake and high cervical cancer incidence were completed online by parents of
adolescents (N=357). Bivariate logistic regressions examined factors impacting HPV vaccine
uptake among Latino adolescents ages 12-18; the moderating effect of parental acculturation
was explored. Multivariable logistic regressions included factors significant at p<.01 in bivariate
analyses, stratifying by acculturation.
Results: 151 parents of children aged 12 and older identified as Latino; 72% were low
acculturated and 28% had high acculturation scores. Factors associated with HPV vaccination
in bivariate analyses included: HPV vaccine awareness (OR= 2.8, 95%CI:1.4,5.7), HPV vaccine
hesitancy (OR=2.1, 95%CI:0.9,4.9), Tdap uptake (OR= 2.6, 95%CI:1.1,5.7), parental female
gender (OR= 2.4, 95%CI:0.8, 6.9), adolescent female gender (OR= 2.5, 95%CI1.3,4.7), and
provider recommendation to vaccinate against HPV (OR= 17.8, 95%CI:7.9,40.6). Multivariable
models including these variables found that parents with low acculturation were more likely to
report a child vaccinated against HPV if the parent was female (OR=5.4, 95%CI:1.2,23.9), a
63
provider recommended HPV vaccination (OR=16.3, 95%CI:4.9,53.8), and their children
received Tdap vaccination (OR=3.3, 95%CI: 1.1,10.1). Among parents with high acculturation
only a provider recommendation of HPV vaccination was significantly associated with increased
HPV vaccine uptake (OR=71.0, 95%CI:5.7,71.0).
Conclusions: Our findings align with research identifying provider recommendations as the most
important factor impacting adolescent HPV vaccination. It contributes to the literature by
confirming the positive impact of provider recommendations among Latino acculturation
subgroups, highlighting the need to invest in interventions to improve provider recommendations
for HPV vaccination. More education is needed among low acculturated male parents about the
importance of HPV vaccination; coadministration with Tdap vaccination presents an opportunity
to improve HPV vaccination among this group.
64
BACKGROUND
While national averages of Human Papillomavirus (HPV) vaccine initiation are higher among
Latinos than in other racial/ethnic groups, disparities in uptake exist among subgroups of Latino
adolescents.
8,44,46
As HPV vaccination is regularly recommended for adolescents ages 11-12
(with expanded eligibility for ages 9-45), vaccination decisions for this population are made by
their parents and caregivers, and as such a substantial body of literature has explored the
factors impacting HPV vaccine uptake among parents of Latino adolescents at the individual
and interpersonal levels. However, little research has focused on HPV vaccine uptake among
Latinos residing in communities at high risk for cervical cancer (i.e., high cervical cancer
incidence and low rates of HPV vaccination).
8,45,191
Several parental individual level characteristics has been examined to understand uptake of
HPV vaccination in Latino adolescents. Studies examining knowledge about the HPV vaccine
and HPV-associated diseases among Latino parents of adolescents have shown mixed results
in different samples of Latino parents. While some research has found high levels of knowledge
in Latino communities,
8,81,82
others have reported low knowledge,
8,45,75-80,192
and multi-ethnic
samples have found that knowledge about HPV is lower among Latinas than non-Hispanic white
women.
8
Level of acculturation, English proficiency, and length of time in the U.S. have all been
found to impact HPV vaccine uptake among adolescents of Latino parents, but the strength and
direction of the relationship has been mixed depending on the location of the study (e.g., Texas,
California, Florida, Puerto Rico, US-Mexico border communities, etc.), highlighting the
heterogeneity of Latino sub-populations in the United States.
38,46,65,66,84
HPV vaccine uptake has been associated with several other individual-level sociodemographic
characteristics, including poverty, insurance status, maternal education, and a child’s number of
siblings.
8,39,45,65,66
Parental and adolescent health-seeking behavior has also been found to
65
impact HPV vaccination, with higher rates among adolescents whose parents engaged in
preventive healthcare services as well as adolescents engaged in the healthcare system and
those receiving other adolescent immunizations.
65,66
Vaccine hesitancy and medical mistrust are interrelated but distinct and potentially important
factors impacting parental HPV vaccine decision-making. While aspects of vaccine hesitancy
can be related to medical mistrust, it can also be associated with issues related to knowledge,
concerns about vaccine safety and effectiveness, and social norms.
193,194
Conversely, medical
mistrust can be associated with numerous issues beyond vaccinations.
195
The roll out of
COVID-19 vaccines has also exacerbated medical mistrust and hesitancy among some groups,
60-62
but our information about HPV vaccine hesitancy in Latino communities is limited; while
Latino parents of adolescents report overall positive attitudes about the HPV vaccine, this has
not always been associated with higher uptake of HPV vaccines among Latino sub-
groups.
8,42,43,45,74,90-93
At the interpersonal level, relationships with providers, family, and friends all have been shown
to impact HPV vaccine uptake among parents of Latino adolescents. While provider
recommendation is the most frequently reported predictor of HPV vaccine uptake in
Latinos,
8,75,84,86
there are reports of lower provider recommendations to vaccinate against HPV
among Latino parents than among their non-Hispanic peers.
8
Other factors associated with low
HPV vaccine uptake among Latinos include fears of sexual activity in their children, concerns
about side effects, and exposure misinformation about the HPV vaccine, which can be
reinforced through interactions with friends and family members.
8,33,94,196
While we know about how individual and interpersonal level factors operating on their own
impact HPV vaccine uptake among Latino parents of adolescents, little is known about the
66
effect that multiple simultaneous barriers to vaccination have on adolescent uptake of the HPV
vaccine. Barriers to accessing care can have an additive effect, worsening access to preventive
care services for vulnerable groups,
197
and individuals may face multiple barriers to HPV
vaccination at the same time,
45,65,66
making it important for us to understand the impact of
multiple barriers to HPV vaccination on adolescent HPV vaccine uptake. Index measures have
been previously utilized to summarize the impact of multiple risk factors on disparities in
pediatric healthcare utilization,
197,198
but to our knowledge so far have not been used to assess
the impact of exposure to multiple barriers to HPV vaccination among Latino parents on HPV
vaccine uptake among their adolescent children.
Furthermore, while barriers and facilitators to adolescent HPV vaccination have been identified
among Latino parents overall,
45,65,66
we still do not fully understand the factors impacting HPV
vaccine uptake decision-making among parents of Latino adolescents living in communities at
high risk of cervical cancer (defined as an area with high cervical cancer incidence and low HPV
vaccination). Using the Social Ecologic Model as a framework, the aim of Study 2 will be to
identify the interpersonal and individual level factors associated with low HPV
vaccination uptake among Latinos residing in communities with high cervical cancer
risk.
Acknowledging that barriers and facilitators to HPV vaccine uptake can occur together,
45,65,66
we
hypothesized that Latino parents reporting multiple barriers to HPV vaccination would have
lower odds of having an adolescent who initiated the HPV vaccine series (Hypothesis 2).
METHODS
Overview
67
Study 2 performed secondary analysis of survey data collected as part of the NCI-funded
Administrative Supplement to the USC Norris Comprehensive Cancer Center (NCCC),
“Addressing HPV vaccine hesitancy in regions with low adolescent HPV vaccine uptake”, with
parents of adolescent of the unit of analysis.
43
Data Source
Parents of high and middle school children were recruited over two weekends in March 2021,
through a collaboration with USC’s Leslie and William McMorrow Neighborhood Academic
Initiative (NAI), an academic enrichment program for minority families in Los Angeles supporting
low-income schools located within the communities adjacent to the USC campuses and the
USC NCCC. Eligibility for this study included being the parent or guardian of an adolescent
aged 9-17 enrolled in an NAI school; ability to complete the survey in English, Spanish or
Mandarin; and participating in an NAI parent workshop during study recruitment in March 2021.
Surveys were self-administered in English, Spanish, and Chinese using REDCap during two
weekend virtual parent workshops hosted by NAI. The study survey assessed topics
surrounding HPV vaccine uptake, as well as knowledge, attitudes, and barriers to the HPV
vaccine; acculturation, parental, and adolescent sociodemographic information were also
collected. Parents who participated in this study received a $25 gift card as an incentive for
participation. This study was approved by the USC Institutional Review Board (UP-20-01003).
Preliminary analysis of Los Angeles Surveillance, Epidemiology, and End Results (SEER)
Program data identified the community surrounding the NCCC as a cervical cancer hotspot
(Figure 14.);
14
previous maps of self-reported HPV vaccination data from the 2018 LACHS
identified this as a low HPV vaccine uptake area (Figure 15). As the NCCC catchment area was
the target location for the Supplement study, surveys from this study were used to represent
68
areas of cervical cancer high risk. Study 2 analyzed surveys from the 260 parents in the study
who identified as Latino. Study 3 of the proposed dissertation will also use data from this
source.
Figure 14. Hot and cold spots of cervical cancer incidence for all race/ethnicities in Los Angeles
County (LA SEER, 2000-2018).
Figure 15. HPV Vaccine Initiation among adolescents in Los Angeles County (Los Angeles
County Health Survey, 2018).
Table 11. Study 2 Measures
USC NCCC
69
VARIABLE
LEVEL OF
INFLUENCE
Adolescent aged 9-17 with ≥ 1 dose of HPV vaccine (Y/N) Individual - Outcome
Acculturation (Brief Acculturation Scale for Hispanics)
199
Individual
Vaccine hesitancy (HPV Vaccine Hesitancy Scale)
194
Individual
Knowledge about HPV Infection and HPV Vaccine Individual
Awareness of HPV Infection and HPV vaccination Individual
Parental sociodemographic characteristics (sex, education,
income)
Individual
Adolescent sociodemographic characteristics (age, sex) Individual
Adolescent immunizations (TDAP and influenza) Individual
Adolescent healthcare access (insurance, usual source of care) Individual
Medical Mistrust
195
Interpersonal
Exposure to negative information about HPV vaccine Interpersonal
Provider recommendation for HPV vaccination Interpersonal
Study Variables
Outcome Variable
A survey question asked parents to state whether their children had received at least one dose
of the HPV vaccine. This dichotomized (Yes/No) assessment of adolescent initiation of the HPV
vaccine series will be our outcome of interest.
Individual Level Predictors of Interest
Acculturation. A modified version of the 4-item Brief Acculturation Scale for Hispanics
(BASH)
199
was included in the survey, and responses to this scale were used to assess parental
acculturation. Scale items asked respondents about their language use at home and with
friends, as well as their language preferences for reading and thinking. Response options in the
original scale included: “only in Spanish”, “more in Spanish than English”, “both equally”; “more
English than Spanish”; and “only English”. Given that the survey was administered to English
and Chinese speakers as well, scale response choices were modified to replace the original,
Spanish-specific answers with “your native language”. Item responses were averaged for a total
scale score ranging from 1 to 5, with higher scores denoting more acculturation. Following the
70
definition of Mills and colleagues, individuals with scores above 3.25 were considered to be
highly acculturated.
199
HPV Vaccine Hesitancy. The study survey assessed vaccine hesitancy using the 9-item HPV
Vaccine Hesitancy Scale. Szilagyi and colleagues adapted the WHO SAGE Vaccine Hesitancy
Scale, developed by the World Health Organization to assess hesitancy and skepticism
surrounding vaccination behavior, to examine hesitancy related to the HPV vaccine.
194,200
The
scale asks participants to rate their agreement or disagreement (using a 4-point Likert scale,
without a neutral response option) to statements denoting a series of attitudes about the HPV
vaccine, such as “The HPV vaccine is effective”; “The HPV vaccine is beneficial for my
child/adolescent”; “The information I receive about the HPV vaccine from my adolescent’s
healthcare provider is reliable and trustworthy.”; and “The HPV vaccine has not been around
long enough to be sure it’s safe.” Scale scores were calculated by averaging responses to each
item and ranged from 1 to 5, with higher scores denoting more HPV vaccine hesitancy.
Knowledge about HPV Infection and HPV Vaccine. The study survey assessed parents’
knowledge about HPV and HPV vaccination, which were assessed as potential predictors of
adolescent HPV vaccine uptake. Parents were asked to respond whether they agreed or
disagreed with 7 statements: that HPV could cause cervical cancer, that it could cause oral
cancer; that HPV infection is rare; that HPV is a sexually transmitted infection; that males
cannot get infected with HPV; that HPV could be asymptomatic; and that their children may be
at risk of acquiring HPV later in their lifetimes. A knowledge score was constructed by adding
correct responses to each of these statements. Knowledge scores ranged from 1 to 7, with
higher numbers denoting more knowledge about HPV.
201
While this instrument has not been
previously psychometrically validated, it included a subset of questions from a validated
71
instrument
202
has been used in the literature to assess parental knowledge of HPV vaccination.
201
Awareness of HPV Infection and HPV Vaccine Awareness. Parents were asked whether
they had ever heard about HPV and if they knew about the HPV vaccine (answer choices
included “Yes” and “No”). Responses to these binary questions were used to assess HPV and
HPV vaccine awareness among our sample.
Parental and Adolescent Characteristics. We explored the effect of parental and adolescent
demographic characteristics on adolescent HPV uptake. In particular, we examined parental
gender, age, insurance coverage type, education, income, and nativity, as well as adolescent
age, gender, and insurance coverage.
Adolescent Immunization Uptake. Parents were asked whether their children had ever
received a TDAP vaccine, and whether their child had received an influenza vaccine (“flu shot”)
in the past 12 months. Responses to these dichotomized (Yes/No) measures were used to
assess adolescent uptake of other age-appropriate immunizations.
Adolescent Healthcare Utilization. Two variables were used to assess adolescent healthcare
access: adolescent insurance and adolescent usual source of care. Parents were asked to
identify whether their adolescent had any health insurance coverage. Answer choices included:
no insurance; employer provided private insurance; self-purchased private insurance; and
Medicaid (Medi-Cal)/Children’s Health Insurance Program (CHIP). The two private insurance
response options were combined to simplify answer choices into no insurance, private
insurance, and public insurance coverage.
72
Parents were asked to indicate where their children usually received care. Answer choices
included: doctor’s office; emergency room; health department clinic; school clinic; clinic or health
center; and no usual source of care.
Interpersonal Level Predictors of Interest
Medical Mistrust. The study survey included the Group-Based Medical Mistrust scale to assess
medical mistrust. This 12-item scale was originally validated to assess medical mistrust among
African American and Latina women seeking mammography services in New York City. The
scale asks respondents to use a 5-point Likert scale (ranging from “Strongly Agree” to “Strongly
Disagree”) to express their agreement or disagreement with a series of statements describing
experiences of perceived suspicion, hostility, or discrimination in their interactions with
healthcare practitioners. Scale items were summed to create scale scores ranging from 12 to
60, with higher scores indicating more medical mistrust.
195
We designated individuals with
response scores one or more standard deviations above the sample mean as experiencing high
medical mistrust, compared to parents with mean scores in this scale.
Negative Information About HPV Vaccine. Study participants were asked to respond to the
question: “Have you ever received or heard negative information about HPV vaccines?”. This
dichotomized variable (Yes/No) was used to measure parental exposure to negative information
about the HPV vaccine
Provider Recommendation to Vaccinate. All survey parents were asked the question: “Has a
doctor or health care professional ever recommended that your son/daughter receive HPV
shots?” Dichotomized parental responses to this question (Yes/No) were used to assess parent-
reported provider recommendation of the HPV vaccine.
73
Analytic Approach
Summary statistics were used to examine sociodemographic characteristics and distribution of
predictors of interest among the study sample, as well as among low and high acculturation
subgroups. We then used independent T-tests, Chi-square, and Fisher’s Exact Test to explore
the differences in sociodemographic characteristics, exposure to barriers, and HPV vaccine
uptake between low and high acculturated Latinos in our study sample. Continuous variables
were standardized using the min-max technique because the data contained no extreme
values.
203
To address Hypothesis 2, multivariable logistic regression models were performed to explore
the relationship between our outcome variable and potential barriers to adolescent HPV
vaccination at the individual (low acculturation, vaccine hesitancy, negative HPV vaccine
knowledge, attitudes, and beliefs, lack of other adolescent vaccines, lack of adolescent usual
source of care, lack of insurance coverage) and interpersonal levels (medical mistrust, exposure
to negative information about the HPV vaccine, lack of provider recommendation for the HPV
vaccine); our models controlled for parental and adolescent sociodemographic characteristics.
Given the diverse impact that acculturation has been shown to have on health behaviors
broadly
54-59,204
and HPV vaccination in particular,
38,46,84,85
we used an interaction term to
examine the moderating effect of acculturation (high vs. low) on the relationship between
potential barriers and HPV vaccine uptake. To explore the cumulative impact of these barriers
on lack of adolescent HPV vaccine initiation, we created a measure that assessed how many of
the identified, statistically significant (α= 0.05) barriers were present in each respondent in our
sample and performed a logistic regression of this barrier “index” measure and adolescent HPV
vaccine uptake.
74
We explored potential collinearity among predictors using Pearson’s Correlation Coefficients
and Variance Inflation Factors (VIF). Variables with Pearson’s Correlation Coefficients above
0.7 or with VIF’s greater than 5 were not included in the same models. All data management
and analyses were conducted in SAS statistical software version 9.4 (SAS Institute Inc).
RESULTS
Sample description
Of the 357 parents who completed the online survey, 260 (73%) identified as Latino,
205
which is
higher than the LAC county Latino population (49%).
206
Given that HPV vaccination is routinely
recommended for children starting at 11 years old, 103 parents with children younger than 11
were removed from our sample. A total of 157 parents identified as Latino and had children
ages 11 or older. Of these, 6 individuals had no data available on HPV vaccine uptake, our
outcome variable. Given that the number of missingness in the sample was small (N=6, 3.8%),
a complete case analysis was performed; the remaining 151 Latino parents of adolescents aged
11 and older with data available on HPV vaccine uptake was used as our analytic sample.
We explored the sociodemographic and vaccination uptake characteristics of our sample to
understand the makeup of this sample of Latino parents residing in a community at high risk of
cervical cancer. Survey language response was almost evenly split, with 55% of parent
respondents completing the survey in English and 45% in Spanish. Over two-thirds of the
sample was non-US born (68%), and almost three-fourths had low acculturation scores (72%).
Most of the respondents were aged 41-50 (50%), female (89%), had a high school education or
less (56%), and were publicly insured (45%). Additionally, 48% of participants reported incomes
below $40,000.
75
Most adolescents for whom data was reported were 14-17 years old (58%), were publicly
insured (73%), reported a doctor’s office as their usual source of healthcare (74%), and were up
to date with Tdap (77%) and influenza immunizations (57%). Only 1% of respondents reported
having an adolescent with no usual source of care. A detailed breakdown of sample
characteristics appears in Table 12.
Parent-reported adolescent vaccine uptake in our sample was 54.3% (N=82). Parental
awareness of HPV and the HPV vaccine were high with 78% and 70% of parents reporting
awareness, respectively. The mean score of the constructed knowledge scale among the
sample was 3.9 (SD=2.4; scale range= 0-7). The knowledge scale item with most correct
responses was “My child can get HPV later in life” (64% correct responses), while the item with
most incorrect responses was “HPV causes oral cancer” (61% incorrect responses). The full
distribution of item responses appears in Table 12.
Parental HPV vaccine hesitancy was low in this group, with 82% of parents reporting low scores
in the HPV Vaccine Hesitancy scale, and most participants did not report being exposed to
negative information about the HPV vaccine (89%). The mean medical mistrust score was 26.7
(SD=9.4), which was above of the sample scale range mid-point (sample GBMMS scale
range=12-54). More than half of parents reported having received a recommendation for HPV
vaccination from a medical provider (57%).
Table 12. Study 2 sample characteristics.
Frequency (%)/
Mean (SD)
OUTCOME MEASURE
Adolescent HPV vaccine initiation
Yes
No
82 (54.3)
69 (45.7)
SOCIOECOLOGICAL MODEL – INDIVIDUAL LEVEL
LACK OF KNOWLEDGE & AWARENESS
HPV causes cervical cancer
76
Incorrect
Correct
HPV causes oral cancer
Incorrect
Correct
HPV is rare
Incorrect
Correct
HPV is an STI
Incorrect
Correct
Males can’t get HPV
Incorrect
Correct
HPV is asymptomatic
Incorrect
Correct
My child can get HPV later in life
Incorrect
Correct
HPV Awareness
No
Yes
HPV Vaccine awareness
No
Yes
HPV Knowledge
Scale Mean (SD)
60 (39.7)
91 (60.3)
92 (60.9)
59 (39.1)
78 (51.7)
73 (48.3)
61 (40.4)
90 (59.6)
60 (39.7)
91 (60.3)
68 (45.0)
83 (55.0)
54 (35.8)
97 (64.2)
35 (22.3)
122 (77.7)
46 (30.5)
105 (69.5)
3.87 (2.44)
HPV VACCINE HESITANCY
Parental HPV vaccine hesitancy
High (Score 3-5)
Low (Score 1-<3)
28 (18.5)
123 (81.5)
ACCULTURATION
Survey language
English
Spanish
Nativity
US Born
Non-US Born
Prefer not to answer
Acculturation
High (<3.25-5)
Low (1-3.25)
83 (55.0)
68 (45.0)
37 (24.5)
103 (68.2)
11 (7.3)
42 (27.8)
109 (72.2)
LACK OF ADOLESCENT IMMUNIZATIONS
Tdap
No
Yes
Influenza
No
Yes
33 (22.6)
113 (77.4)
65 (43.0)
86 (57.0)
PARENTAL DEMOGRAPHIC CHARACTERISTICS
Age
30-40 years
41- 50 years
> 50 years
42 (28.0)
75 (50.0)
33 (22.0)
77
Gender
Male
Female
Insurance type
Private health insurance
Medicaid/Medicare
Uninsured/Other
Education
High School graduate or less
More than High School
Prefer not to answer
Income
0-39,999
40,000+
17 (11.3)
134 (88.7)
50 (31.9)
62 (44.9)
39 (23.2)
84 (55.6)
58 (38.4)
9 (6)
73 (48.3)
78 (51.7)
ADOLESCENT DEMOGRAPHIC CHARACTERISTICS
Age
11-13 years
14-17 years
Gender
Male
Female
Insurance Type
Private health insurance
Medicaid/CHIP
Uninsured/Other
Usual source of care
Doctor's office only
Health Department or School Clinic only
Multiple sources of care
No Usual Source of Care
63 (41.7)
88 (58.3)
76 (50.3)
75 (49.7)
36 (24.2)
108 (72.5)
5 (3.4)
111 (73.5)
29 (19.2)
9 (6)
2 (1.3)
SOCIOECOLOGICAL MODEL – INTERPERSONAL LEVEL
RELATIONSHIP WITH PROVIDER
Medical Mistrust
Mean score (SD)
Provider Recommendation of HPV vaccine
No
Yes
26.68 (9.37)
64 (42.4)
87 (57.6)
SOCIAL INTERACTIONS
Exposure to HPV Negative Information
Yes
No
17 (11.3)
134 (88.7)
Acculturation Levels
Our study focused on understanding the factors impacting adolescent HPV vaccination in a
Latino community at high risk for cervical cancer; we found broad sociodemographic differences
in Latino parents with high and low levels of acculturation.
78
Low acculturated parents were more likely to respond to the survey in Spanish (60% vs. 7%,
p<0.01) and to have been born outside of the United States (76% vs. 48%, p<0.01) than parents
with high levels of acculturation. Parents with low levels of acculturation were also less likely to
have private insurance coverage (22% vs. 62%, p<0.01), more likely to have a high school
degree or less (65% vs. 31%, p<0.01), and to have annual incomes below $40,000 (56% vs.
29%, p<0.01). Their children were more likely to have public insurance coverage (78% vs. 60%,
p=0.05) and to use a health department, clinic, or health center as their usual source of care
(24% vs. 7%, p=0.03) than the children of high acculturated parents.
While high acculturated parents fared better off in socioeconomic terms than their low
acculturated peers, their children’s HPV vaccination rates were not significantly better than
those of low acculturated parents. Both groups of parents were also similarly likely to have a
provider recommend the HPV vaccine. However, high acculturated parents were more likely to
have a child who had received the Tdap vaccine (90% vs. 72%, p=0.02).
HIGH
ACCULTURATION
(N=42)
LOW
ACCULTURATION
(n=109)
Frequency (%)/
Mean (SD)
Frequency (%)/
Mean (SD)
p-value
OUTCOME MEASURE
Adolescent HPV vaccine initiation
Yes
No
23 (54.8)
19 (42.2)
59 (54.1)
50 (45.9)
0.94
SOCIOECOLOGICAL MODEL – INDIVIDUAL LEVEL
LACK OF KNOWLEDGE & AWARENESS
HPV causes cervical cancer
Incorrect
Correct
HPV causes oral cancer
Incorrect
Correct
HPV is rare
Incorrect
Correct
14 (33.3)
28 (66.7)
29 (69.1)
13 (31.0)
20 (47.6)
22 (52.4)
46 (42.2)
63 (57.8)
63 (57.8)
46 (42.2)
58 (53.2)
51 (46.8)
0.32
0.20
0.54
Table 13. Study 2 sample characteristics by acculturation level.
79
HPV is an STI
Incorrect
Correct
Males can’t get HPV
Incorrect
Correct
HPV is asymptomatic
Incorrect
Correct
My child can get HPV later in life
Incorrect
Correct
HPV Awareness
No
Yes
HPV Vaccine awareness
No
Yes
HPV Knowledge
Scale Mean (SD)
18 (42.9)
24 (57.1)
11 (26.2)
31 (73.8)
14 (33.3)
28 (66.7)
11 (26.2)
31 (73.8)
6 (14.3)
36 (23.8)
8 (19.1)
34 (81.0)
4.2 (2.5)
43 (39.5)
66 (60.6)
49 (45.0)
60 (55.1)
54 (49.5)
55 (50.5)
43 (39.5)
66 (60.6)
27 (24.8)
82 (75.2)
38 (34.9)
71 (64.1)
3.7 (2.5)
0.70
0.03
0.07
0.12
0.16
0.06
0.26
HPV VACCINE HESITANCY
Parental HPV vaccine hesitancy
High (Score 3-5)
Low (Score 1-<3)
10 (23.8)
32 (76.2)
18 (16.5)
91 (83.5)
0.30
ACCULTURATION
Survey language
English
Spanish
Nativity
US Born
Non-US Born
Prefer not to answer
39 (92.9)
3 (7.1)
22 (52.4)
20 (47.6)
0 (0)
44 (40.4)
65 (59.6)
15 (13.8)
83 (76.2)
11 (10.1)
<0.01
<0.01
LACK OF ADOLESCENT IMMUNIZATIONS
Tdap
No
Yes
Missing
Influenza
No
Yes
4 (9.5)
37 (88.1)
1 (2.4)
17 (40.5)
25 (59.5)
29 (26.6)
76 (69.7)
4 (3.7)
48 (44.0)
61 (56.0)
0.02
0.69
PARENTAL DEMOGRAPHIC CHARACTERISTICS
Age
30-40 years
41- 50 years
> 50 years
Missing
Gender
Male
Female
Insurance type
Private health insurance
Medicaid/Medicare
Uninsured/Other
Education
High School graduate or less
16 (38.1)
17 (40.5)
8 (19.1)
1 (2.4)
3 (7.1)
39 (92.9)
26 (61.9)
13 (31.0)
3 (7.1)
13 (31.0)
26 (23.9)
58 (53.2)
25 (22.9)
0 (0)
14 (12.8)
95 (87.2)
24 (22.0)
49 (45.0)
36 (33.0)
71 (65.1)
0.18
0.32
<0.01
<0.01
80
More than High School
Prefer not to answer
Income
0-39,999
40,000+
28 (66.7)
1 (2.4)
12 (28.6)
30 (71.4)
30 (27.5)
8 (7.3)
61 (56.0)
48 (44.0)
<0.01
ADOLESCENT DEMOGRAPHIC CHARACTERISTICS
Age
11-13 years
14-17 years
Gender
Male
Female
Insurance Type
Private health insurance
Medicaid/CHIP
Uninsured/Other
Missing
Usual source of care
Doctor's office only
Health Department, Clinic or Health Center only
Multiple sources of care
No Usual Source of Care
17 (40.5)
25 (59.5)
25 (59.5)
17 (40.5)
16 (38.1)
25 (59.5)
1 (2.4)
0 (0)
37 (88.1)
3 (7.1)
1 (2.4)
1 (2.4)
46 (30.5)
63 (57.8)
51 (46.8)
58 (53.2)
20 (18.4)
83 (76.2)
4 (3.7)
2 (1.8)
74 (67.9)
26 (23.9)
8 (7.3)
1 (2.4)
0.85
0.16
0.05
0.03
SOCIOECOLOGICAL MODEL – INTERPERSONAL LEVEL
RELATIONSHIP WITH PROVIDER
Medical Mistrust
Mean score (SD)
Provider Recommendation of HPV vaccine
No
Yes
25.5 (9.4)
16 (38.1)
26 (61.9)
27.1 (9.3)
48 (44.1)
61 (56.0)
0.35
0.51
RELATIONSHIP WITH FAMILY & PEERS
Exposure to HPV Negative Information
Yes
No
8 (19.1)
34 (81.0)
9 (8.3)
100 (91.7)
0.06
Regression Models
Our analyses found differences in the distribution of barriers to HPV vaccination and
sociodemographic characteristics between parents with and without adolescents who had
initiated the HPV vaccine series. Parents who reported a vaccinated child were more likely to
have previously heard about the HPV vaccine (OR=2.8, 95% CI: 1.35-5.68), to have an
adolescent who received Tdap immunizations (69% vs 85%, p=0.02), to have a female
adolescent (39% vs. 60%, p=0.01), and to have received a provider recommendation to
vaccinate against HPV (85% vs. 25%, p<0.01). The results from all bivariate logistic regression
analyses appear on Table 14.
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Table 14. Logistic regression models of adolescent HPV vaccine uptake.
Bivariate Model Multivariable Model
OR 95% CI p-value aOR 95% CI p-value
INDIVIDUAL LEVEL
Lack of Knowledge &
Awareness
HPV Knowledge Scale
1.06 (0.93, 1.21) 0.39
HPV Awareness
No Ref
Yes 1.85 (0.85, 4.03) 0.12
HPV Vaccine Awareness
No Ref
Yes 2.77 (1.35, 5.68) 0.01 0.63 (0.22, 7.80) 0.38
Vaccine Hesitancy
HPV Vaccine Hesitancy
High Ref Ref
Low 2.11 (0.91, 4.88) 0.08 2.89 (0.93,9.02) 0.07
Acculturation
Survey Language
English Ref
Spanish 1.25 (0.66, 2.39) 0.50
Nativity
Non-Us Born
Ref
US Born
1.15 (0.54, 2.44) 0.73
Acculturation
High
1.03 (0.50, 2.10) 0.94
Low
Ref
Lack of Adolescent Immunizations
Tdap
Yes 2.55 (1.14, 5.69) 0.02 2.49 (0.87, 7.15) 0.09
No Ref Ref
Flu
Yes 1.43 (0.75, 2.74) 0.28
No Ref
Parent Demographic Characteristics
Age
30-40 years Ref
41- 50 years 1.44 (0.67, 3.09) 0.15
> 50 years 0.67 (0.27, 1.68) 0.68
82
Gender
Male Ref
Ref
Female 2.40 (0.84, 6.88) 0.10
4.58 (1.17, 17.2) 0.03
Education
High School graduate or less 0.89 (0.46, 1.75) 0.46
More than High School Ref
Unknown/Don't know/Prefer not
to answer
1.63 (0.37, 7.13) 0.42
Income
0-39,999 0.93 (0.49,1.77) 0.83
40,000 or greater Ref
Adolescent Demographic Characteristics
Age
11-13 years Ref
14-17 years 1.14 (0.60, 2.19)
0.68
Gender
Male Ref Ref
Female 2.46 (1.27, 4.74)
0.01
1.46 (0.61, 3.47) 0.30
Insurance Type
Private health insurance Ref
Medicaid/CHIP 0.71 (0.33, 1.54) 0.87
Uninsured/Other
0.42
(0.06, 2.87) 0.46
Usual source of care
Doctor's office only Ref
Health Department/ Clinic or
health center
0.85 (0.37, 1.92) 0.92
Multiple sources of care 0.63 (0.16, 2.48) 0.70
No Usual Source of Care 0.79 (0.05, 12.96) 0.99
INTERPERSONAL LEVEL
Relationship with Provider
Medical Mistrust 1.01 (0.98, 1.05) 0.46
Provider recommendation
Yes 17.84 (7.85, 40.57) <0.01 21.48 (7.72, 59.75) <0.01
No
Ref
Ref
Relationship with Family & Peers
HPV Negative Information
Yes Ref
No 0.80 (0.29, 2.26) 0.69
83
A multivariable model was constructed including all variables significantly associated with HPV
vaccine uptake at p<0.1, which included: HPV vaccine awareness (OR= 2.8, 95% CI: 1.4, 5.7;
p=0.01), HPV vaccine hesitancy (OR=2.1, 95% CI: 0.9, 4.; p=0.08), Tdap (OR= 2.6, 95% CI:
1.1, 5.7; p=0.02), parental gender (OR= 2.4, 95% CI: 0.8, 6.9; p=0.10), adolescent gender (OR=
2.5, 95% CI 1.3, 4.7; p=0.01), and provider recommendation to vaccinate against HPV (OR=
17.8, 95% CI: 7.9, 40.6; p<0.01).
Before performing the multivariable analyses, we explored the correlations between the
proposed predictor outcomes. No correlations emerged above our stipulated criteria of a
Pearson’s Correlation Coefficient higher than 0.7. The largest correlation identified was between
provider recommendation and awareness of the HPV vaccine, but it was far below our stated
standard (0.42 < 0.7). A list of all correlations appears on Table 15.
Table 15. Pearson Correlation Coefficients of proposed predictors
HPV
Vaccine
Awareness
HPV
Vaccine
Hesitancy
Tdap Parental
Gender
Adolescent
Gender
Provider
recommendation
of HPV Vaccine
HPV Vaccine
Awareness
1
HPV Vaccine
Hesitancy
0.02 1
Tdap 0.14 0.05 1
Parental Gender 0.13 0.06 0.06 1
Adolescent
Gender
-0.14 0.07 -0.12 -0.10 1
Provider
recommendation
of HPV Vaccine
0.42 -0.07 0.13 -0.01 -0.24 1
After including all the variables in a logistic regression model, only provider recommendation to
vaccinate against HPV (OR=18.1, 95% CI:6.6, 49.5), p<0.01) and parental female gender
84
(OR=4.6, 5% CI: 1.2, 17.2; p=0.03) were significantly associated with higher odds to vaccinate
against HPV. Full model results appear on Table 14.
Index
Given that only two of all the factors explored as potential barriers to HPV vaccination were
significantly associated with uptake, we created a barrier index including all barriers to HPV
vaccine uptake included in the survey. We defined the following as barriers to HPV vaccine
uptake: knowledge scale means below the sample mean; no awareness of HPV; no awareness
of the HPV vaccine; high HPV vaccine hesitancy; low acculturation; no Tdap vaccination; no
Influenza vaccination; medical mistrust scale scores above the sample mean; no provider
recommendation to vaccinate against HPV; and exposure to negative information about the
HPV vaccine. Given the sample’s sociodemographic similarities, and that only parental gender
and teen sex was significantly different between vaccinated and unvaccinated groups (the effect
for teen sex 1 disappeared in the multivariable model), sociodemographic characteristics
associated with HPV vaccine uptake were not included in the barrier index.
We found an additive effect of exposure to barriers to HPV vaccination and HPV vaccine
uptake, with individuals with more reported barriers to HPV vaccination being less likely to have
an adolescent that had initiated the HPV vaccine series (OR=0.66, 95% CI: 0.54, 0.80; p<0.01).
However, we were concerned about the reliability of an index that only included one barrier
significantly associated with HPV vaccine uptake.
Effect Modification
We explored the impact of acculturation status on the relationship between HPV vaccine uptake
and all previously defined barriers to HPV vaccine uptake. To account for the effect of multiple
85
testing, we performed a Bonferroni correction and adjusted our significance value accordingly:
since we explored 9 interactions with HPV vaccine uptake, we set our significance at p<0.006
(α=0.05/9). We found a significant interaction between acculturation and provider
recommendation for HPV vaccination (p<0.0001), indicating that the effect of provider
recommendation on HPV vaccine uptake varied by acculturation status.
We therefore stratified our dataset by acculturation status and explored our multivariable logistic
regression model in each dataset. We found that different factors impacted HPV vaccine uptake
in individuals with high and low acculturation status. After adjusting for all variables included in
the model, parents with low acculturation were more likely to report a child vaccinated against
HPV if they were female, had received a provider recommendation to vaccinate against HPV,
and reported that their adolescent had received a Tdap vaccination. Meanwhile, among parents
with high acculturation, only a provider recommendation to vaccinate against HPV was
significantly associated with HPV vaccine uptake.
The magnitude of the effect of provider recommendation was substantially larger among high
acculturated individuals, associated with an over 71 times increased odds of an adolescent
initiating the HPV vaccine series (compared to 16 times increased odds among low acculturated
individuals). Detailed results of the multivariable models in both strata appear on Table 16.
Table 16. Stratified multivariable logistic regression models of HPV vaccine uptake, including
variables significantly associated with HPV vaccine uptake at p<0.1 in bivariate models and the
variance inflation factor (VIF) for each predictor.
Low Acculturation High Acculturation
VIF
OR 95% CI p-value OR 95% CI p-value
HPV Vaccine Awareness 0.68 0.22, 2.15 0.51 0.79 0.04, 16.38 0.88
1.2
HPV Vaccine Hesitancy 2.06 0.52, 8.22 0.3 4.60 0.37, 4.60 0.23
1.0
Tdap Immunization 3.29 1.07, 10.11 0.04* 0.40 0.01, 0.40 0.6
1.0
Parental Gender 5.41 1.23, 23.88 0.03* 2.01 0.02, 2.01 0.76
1.0
Adolescent Gender 1.33 0.49, 3.61 0.58 2.29 0.28, 2.29 0.44
1.1
86
Provider recommendation 16.28 4.93, 53.8 <0.01* 71.02 5.74, 71.02 <0.01*
1.3
* p<0.05
DISCUSSION
This study explored barriers at the individual and interpersonal levels to adolescent HPV
vaccine uptake among a sample of Latino parents of adolescents residing in an area at high risk
for cervical cancer. We found that lack of a provider recommendation for HPV vaccination and
parental male sex were both significantly negatively associated with adolescent HPV vaccine
update, after controlling for HPV vaccine awareness, HPV vaccine hesitancy, adolescent Tdap
uptake, and adolescent gender. Estimates of HPV vaccine uptake among our sample are in line
with those found by local assessments of parent-reported HPV vaccination among Latinos in
Los Angeles
149
and in conflict with national estimates that suggest that HPV vaccine initiation
among Latinos is over 70%.
207
This divergence highlights the need to document HPV vaccine
uptake among Latino sub-groups and across small area geographies.
Furthermore, we found that acculturation level significantly modified the effect of provider
recommendation on HPV vaccine uptake. Our findings align with numerous studies which have
found provider recommendations to be the most important factor impacting adolescent HPV
vaccination,
45,65,66,95,208
and contributes to the literature by confirming the positive impact of
provider recommendations among Latino acculturation subgroups, rather than among non-
Hispanic White or diverse populations; instead of examining Latinos as a homogeneous group.
Provider recommendations can help shape parental attitudes and beliefs about the vaccine as
positive, safe, effective, and necessary, and can also shift subjective norms among parents,
increasing acceptability of the HPV vaccine. Attitudes, beliefs, and subjective norms are all parts
of the Theory of Planned Behavior’s proposed pathway to impacting to impact health behavior
which can impact HPV vaccination intentions and behavior.
155-158,209,210
87
We also found that the positive impact of provider recommendations is more pronounced among
high acculturated parents. (OR=71.0, 95% CI: 5.7-71.0) than among low acculturated parents
(OR=16.3, 95% CI: 4.9-53.8). While female parent sex (OR=5.4, 95% CI: 1.2-23.9) and having
an adolescent who had initiated the Tdap series (OR=3.3, 95% CI: 1.07-10.11) were also
positively associated with HPV vaccine uptake among low acculturated parents, a provider
recommendation to vaccinate was the only factor significantly associated with HPV vaccination
among high acculturated parents. Our bivariate analyses found statistically insignificant but higher
HPV vaccine hesitancy (24% vs. 17%, p=0.30) and more exposure to negative information about
the HPV vaccine (19% vs. 8%, p=0.06) among high acculturated parents, which could suggest
more negative attitudes towards HPV vaccination in this group. Our small sample of high
acculturated parents could explain the lack of statistical significance of these findings, especially
in the case of the marginally significant association with exposure to negative information about
the HPV vaccine. As previous research
73,87,88
has found that medical providers are the most
important source of health information among Latinos, it could be that a provider recommendation
for an HPV vaccine from a trusted source would be more impactful among a more hesitant and
misinformed group, which our results suggest that high acculturated individuals may be. Our
findings confirm previous research that underscores the importance of targeted, culturally specific
interventions to improve HPV vaccine uptake among diverse populations by highlighting how
barriers to HPV vaccination impact adolescent HPV vaccination uptake differently in Latino
acculturation sub-groups (high vs. low acculturation).
65,208
In addition, our results support the importance of interventions focusing on improving provider
recommendations for HPV vaccination among Latino parents, especially high acculturated ones.
They suggest that strategies focusing on improving knowledge, attitudes, or parental
vaccination hesitancy may be less effective than those focusing primarily on strategies to
improve provider recommendations, since our analyses did not find knowledge skills, attitudes,
88
or hesitancy to be significantly associated with HPV vaccine uptake in our sample of high
acculturated Latino parents. This finding is particularly important for Latino-serving vaccination
providers operating within constrained resources within an environment of competing priorities
and can provide guidance to stakeholders making decisions about how to dedicate limited
resources to improving HPV vaccine uptake among Latino parents of adolescents. Our results
provide additional evidence to support the use of interventions such as provider reminders,
electronic health record prompts, and provider communication training all of which have been
found to improve adolescent HPV vaccine uptake.
86,119,209,211-222
While these have not been
tested specifically among Latino parents, these results provide impetus to assess their fidelity
among Latinos, particularly those residing in areas at high risk for cervical cancer. Our hotspot
methodologies could be used to identify the communities in which such interventions should be
tested.
Given the large confidence intervals resulting from our analyses, future research should attempt
to confirm these findings among larger Latino samples with diverse acculturation levels that can
provide statistical stability to the analytic results. Furthermore, examining these results in other
non-urban Latino samples can help us understand the factors impacting parental HPV
vaccination behavior in other Latino sub-groups (e.g., rural communities, East Coast residents,
etc.).
Future research should also focus on understanding provider perspectives on their own HPV
vaccine recommendation practices among parents of Latino adolescents. While some research
has found lower provider recommendation for HPV vaccination in Latino samples,
223,224
more
work should be done to disentangle whether this is due to actual lower provider
recommendations among Latinos or whether it is the result of patient-provider
miscommunications, perhaps accompanied by issues of language barriers. Electronic health
89
record data should be used to explore provider practices of HPV vaccine recommendation in
diverse populations to clarify this phenomenon. Further research should also explore the
implementation of strategies to improve provider recommendations of the HPV vaccine among
providers serving primarily Latino populations to identify trends, intervention effectiveness, and
potential barriers.
Limitations and Study Implications
The results of this study are limited by the fact that no comparative analyses were performed
with other racial/ethnic groups. However, within group comparisons by acculturation level
highlight how factors operating at diverse levels of the socioecological model impact HPV
vaccination differently in each group. Results of this study are also not representative of other
Latino sub-groups because the purpose of this study was to explore in depth a Latino population
at high-risk cervical cancer. Our results cannot be generalized to other Latino populations with
higher acculturation levels, larger proportions of non-us born individuals, or better
socioeconomic characteristics, as well as more rural Latino populations. Our sample size was
small, which creates difficulties for variables with little variation in response choices (such as
variables assessing ‘parental sex’ and ‘exposure the negative information about the HPV
vaccine’), which introduces challenges in the interpretability and reliability of estimates
associated with those variables Our data was collected as part of a cross sectional study, so no
causality can be inferred from our results. Additionally, the study was conducted online in March
of 2021, when many COVID-19 pandemic restrictions were still in place. It is possible that
parents with less computer literacy did not complete the survey, which could have potentially
excluded individuals in need of more support from our results.
90
In terms of our study instrument, our results are limited to populations with access to the internet
and enough technological literacy to participate in virtual workshops and complete a self-
administered survey online. Parents included in our study were already at least receiving some
guidance regarding their children’s education through their participation in the NAI program, so
the factors impacting HPV vaccination among parents with less types of support may be
different. Furthermore, our study excludes any Latinos who do not speak English or Spanish,
such as Latino indigenous immigrants from Mexico, Guatemala, and other parts of Central
America; therefore, our results should not be used to understand the factors impacting HPV
vaccine uptake in such groups. Finally, even though our study instrument was translated by a
translation service with broad experience in community health studies, it is possible that a
different Spanish translation of the instrument would have led to different survey responses
which could have altered our results.
However, we believe that obtaining granular data from Latinos residing in a community at high
risk for cervical cancer is a necessary first step in planning interventions that effectively target
the specific needs of a group that is disproportionally impacted by HPV-associated cancers.
The mixed results from many of the studies that have explored the individual and interpersonal
factors impacting HPV vaccine uptake among Latino parents of adolescents could be reflecting
the heterogeneous nature of this diverse and expanding community in the United States, and
highlight the need to obtain context and community specific information about different Latino
sub-groups, especially in terms of targeting and planning HPV vaccine uptake interventions and
other cancer screening and prevention services.
Our study provides deeper understanding of the factors impacting HPV vaccine uptake in a
community at high risk of cervical cancer, and within a diverse Latino sample with high
proportion of non-US born, low acculturated individuals. These results bring to the foreground
91
the differences in the ways that barriers to HPV vaccination impact uptake behavior among
Latino parents of different acculturation levels, helping us identify opportunities to target HPV
vaccination interventions differently along acculturation levels. Our results suggest that
interventions designed to target Latinos as a homogeneous community may be suboptimal and
ineffective.
92
CHAPTER 5: Study 3: Implementing GIS-Based Multi-Criteria Decision Analysis to Optimize
Delivery of HPV Vaccine Interventions among Latino Communities in Los Angeles
ABSTRACT
Background: Latinas are disproportionally impacted by cervical cancer, making it of paramount
importance to identify ways to target and optimize strategies for improving HPV vaccine rates in
Latino communities. However, scant research has focused on how to identify optimal clinics in
which to implement interventions to improve HPV vaccination among Latino communities at
high-risk for cervical cancer.
Methods: We focused on clinics participating in the Vaccines for Children (VFC) program
located in ZIP code tabulation areas (ZCTAs) in Los Angeles County with >60% Latino
populations, containing a cervical cancer hot spot, and with HPV vaccination uptake rates below
the County average. We used multi-component decision analysis (MCDA) to create scores for
each clinic, integrating data on HPV vaccination (from the California Immunization Record),
factors known to impact HPV vaccine uptake (from Study 1 regression model results),
interventions in place at local clinics to improve HPV vaccination (from phone surveys), and
cervical cancer burden measures (distance from clinic to hot spots; percent of Los Angeles
County cases of cervical cancer; proportion of late-stage cervical cancer cases, from LA SEER)
to calculate MCDA scores. We calculated a population preventable fraction (PPF) to estimate
potential reductions in cervical cancer incidence from locating interventions to improve HPV
vaccination in these clinics, compared to clinics outside these high-risk, Latino areas.
Results: We identified 17 VFC clinics in Latino communities at high risk for cervical cancer.
Among these, MCDA clinic scores ranged from 61-1688, with higher scores denoting better
suitability to implement interventions to improve HPV vaccination. Of the factors included in the
93
final score, largest variation was observed in proportion of late-stage cervical cancer cases in
ZCTA where the clinic was located (46-83). We found a PPF of 0.87 for interventions located in
the high-risk Latino communities, compared with a PPF of 0.66 for interventions located outside
of these communities. Clinic locations and their MCDA scores were visualized in an online
dashboard to allow for dissemination of study results.
Discussion: Our results show that greater population-level cervical cancer reductions can be
obtained by implementing interventions to improve HPV vaccination in clinics located in high-
risk Latino communities. Our scores allow for quantitative comparisons that can allow
stakeholders to identify clinics with greatest potential for population-level cervical cancer
reductions.
94
BACKGROUND
Numerous strategies have been identified to improve adolescent Human Papillomavirus (HPV)
vaccine uptake.
118,211,225
Of special interest from a population-level perspective are those which
operate at the level of clinics or systems which can impact numerous individuals simultaneously.
Clinic-based interventions to improve HPV vaccine uptake have been identified as promising
strategies for population level improvements in HPV vaccine uptake.
226
Significant
improvements in HPV vaccination uptake have been associated with a variety of clinic-based
strategies, such as standing of vaccine orders, coadministration of HPV with other adolescent
immunizations (“bundling”), and provider reminders and prompts.
105-107,109-111,114-119,176,218,227
Latinas are disproportionally impacted by cervical cancer,
2
making it of paramount importance to
identify ways to target and optimize strategies for improving HPV vaccine rates in Latino
communities. However, most empirical research among Latinos so far has focused on
understanding personal preferences or evaluating individual-facing interventions, such as
culturally-relevant education campaigns or navigation programs incorporating promotores de
salud.
97,228-232
Much less attention has been placed on strategies which can improve uptake of
HPV vaccine among Latinos at the clinic level, or on identifying clinics best situated to improve
HPV vaccine uptake among Latinos at a population level. As Latinos are more likely to be
uninsured,
233-236
and uninsurance rates among Latino children have increased dramatically over
the last decade,
237,238
it is especially important that we identify strategies that can help us
identify which clinics participating in public insurance vaccination programs, such as the
Vaccines For Children (VFC) program are best situated to implement interventions to improve
population-level HPV vaccination rates in Latino communities.
95
While the literature examining the effectiveness of clinic-based strategies to improve HPV
vaccination among Latino parents of adolescents is limited,
8
the impact of provider
recommendations of the HPV vaccine on HPV vaccine uptake among parents of adolescents is
well established.
216,239-241
Such impact was highlighted in dissertation Study 2, which found that
a provider recommendation of HPV vaccination to be the strongest factor associated with
uptake of HPV vaccine among high and low acculturated Latino adolescents residing in a
community at high risk of cervical cancer.
Multicriteria Decision Analysis (MCDA) is a type of decision support system that involves a
systematic process of decision-making within the context of competing objectives, alternatives,
and constraints.
242
MCDA can be incorporated into Geographic Information Systems (GIS) to
tackle complex spatial problems incorporating data from multiple sources through a multi-step
process that involves standardization of parameters, weighing of alternatives, and decision
rules.
242,243
In cancer control, MCDA has been utilized to support decision-making surrounding
treatment options,
244,245
cervical cancer screening coverage,
246
and screening strategies for
prostate
247
and colorectal
248
cancers. However, the utilization of MCDA has not yet been
leveraged to optimize our understanding of which clinic sites could be most optimally positioned
to implement an intervention to improve adolescent HPV vaccination in Latino communities.
Since the onset of the COVID-19 pandemic, health dashboards have become popular
mechanisms to display and summarize complex data to support stakeholder and policy
decision-making.
182,249-253
Additionally, mapping has been identified as a powerful strategy to
communicate complex health information to multiple stakeholders, and can serve as a motivator
for community activism and public health planning.
254,255
As such, GIS-based dashboards
incorporating maps and other data visualizations are promising tools to disseminate complex
research results to broad audiences.
96
Therefore, the aim of Study 3 is to identify optimal Latino communities with largest
potential for HPV vaccination uptake improvements through geographic site suitability
techniques and dissemination strategies.
Based on the literature on the effectiveness of clinic-based strategies to improve HPV
vaccination among the general population, we hypothesized that the attributable risk reduction
of cervical cancer would be more than 20% by implementing evidence-based interventions to
improve HPV vaccination at targeted clinics within ZCTAs at high risk for cervical cancer (high
incidence of cervical cancer and low HPV vaccination) with >60% of Latinos rather than at
clinics in ZCTAs with <60% Latinos (Hypothesis 3).
METHODS
Using data from Study 1 (results of geographic weighted regression analysis) and Study 2
(result of multivariable logistic regression analysis) 2 of this dissertation, a Multi-Component
Decision Analysis (MCDA) was used to identify optimal clinics within Latino communities at high
risk of cervical cancer in which to implement HPV vaccination interventions.
Unit of Analysis and Eligibility Criteria
The unit of analysis for Study 3 is clinics. Eligibility criteria for study inclusion comprised of
clinics providing immunization services to adolescents (ages 9-17); listed among Vaccines For
Children immunization providers; and located in ZCTAs with >60% Latino population at high risk
for cervical cancer (in a cervical cancer cluster and low HPV vaccine uptake, as defined in
Study 1).
97
Analytic Approach
Descriptive statistics were used to explore the distribution of our predictors across ZCTAs in Los
Angeles County; independent T and Mann-Whitney U tests (for samples smaller than 10) were
used to explore these characteristics by Latino ethnicity (>60% Latino populations) and cervical
cancer risk.
We used GIS-based MCDA to develop a clinic score which integrated data on clinic strategies
to improve provider recommendation of HPV vaccination (obtained through the phone survey of
eligible clinics), ZCTA-level HPV vaccine uptake, distance from a case-density based hot spot
(from Study 1), ZCTA-level cervical cancer incidence burden, and ZCTA-level
sociodemographic and healthcare utilization variables identified to be significantly associated
(p<0.05) with area-level HPV vaccine uptake, based on Study 1 results.
Addresses for eligible VFC immunization clinics were geocoded in ArcGIS to develop a data
layer with clinic point locations across LAC ZCTAs. We limited the analyses to the locations of
clinics in areas of cervical cancer high risk areas (high incidence, low HPV vaccination) within
Latino residential areas (proportion of the population >60% Latino) and ranked those most likely
to benefit from using clinic-based interventions to improve HPV vaccination.
Following the process proposed by Lalloue and colleagues,
256
we used Principal Component
Analysis (PCA) to identify the correlates of HPV vaccination (per Study 1) that account for the
most amount of variance among all presented variable alternatives to remove redundant
variables. Factors were extracted from the PCA results based on the following criteria: an
eigenvalue above 1, factors appearing above the Scree plot break, and factors with at least 3
associated items. Items were considered to load onto a factor if they had a factor pattern
98
loading over 0.4 (absolute value). PCA results were subsequently used to obtain weights to
create a linear weighted equation which provided a score that contributed to the ranking of each
immunization clinic in our sample.
256,257
To confirm that higher scores were
ArcGIS Pro (version 3.0.3, case-density hot spots, geolocation of clinics, clinic filtering per
eligibility criteria), and SAS (version 9.4, PCA analyses) provided the tools necessary to conduct
theses analysis.
Data Sources
Phone Surveys. A phone survey was conducted to identify the strategies used at each eligible
clinic to improve provider recommendation of the HPV vaccine. Using publicly available phone
listings, clinics were contacted by phone, and asked 1) if they were willing to participate in a
brief survey on HPV vaccination services provided, and 2) to identify a representative best
suited to complete the survey. Informed by Study 2 results, the survey collected data on
strategies the clinic implements to increase provider recommendation of the HPV vaccine. Once
the correct representative was identified, a one-time phone call was scheduled at a convenient
time (as specified by the representative) to administer the survey. Survey completion took
approximately 15 minutes. All data collection activities were approved by the USC Institutional
Review Board (UP-22-00518).
Given that a psychometrically tested assessment of strategies to improve provider
recommendation of HPV vaccination does not exist, a list of questions was developed to identify
the implementation of these strategies among vaccination clinics and medical practices. All
items were designed to be simple and brief, avoiding the use of jargon, poorly defined terms,
double negatives, or double-barreled questions. To ensure content validity, the items developed
for this questionnaire assess domains identified by a search of the peer-reviewed and gray
99
literature.
118,258-262
An open-ended question was added to ensure comprehensiveness of the
domains captured in the assessment. The full questionnaire with instructions for administration
and coding is included in Appendix 2.
Adolescent Immunizations. Data for HPV and Tdap immunizations was obtained from the
California Immunization Registry (CAIR), for individuals ages 9-18 receiving at least one dose of
each vaccine during years 2007-2021.
Factors Impacting ZCTA-level HPV vaccination. Based on the results of our dissertation Study
1, we included characteristics significantly (p<0.05) associated with HPV vaccine uptake in our
analyses using data from the 2010 5-year American Community Survey, including: ZCTA-level
percent Latino, percent non-US born, percent uninsured, percent below the Federal Poverty
Level (FPL), and residential segregation. Residential segregation was assessed by calculating
an Index of Concentration at the Extremes
263
score.
Cancer Incidence. Our analysis includes estimates of cervical cancer incidence developed
during dissertation Study 1 including distance of each clinic from the nearest hot spot, the
percent of LAC cervical cancer (all stages) cases in a ZCTA, and the proportion of late-stage
cervical cancer cases in each ZCTA. The Near Tool in ArcGIS Pro was used to calculate the
distance between each clinic and their nearest cervical cancer hot spot, in meters.
241
This
distance was estimated by finding the perpendicular line between the clinic location and the line
segment of the nearest cervical cancer hot spot boundary (rather than the hot spot center or
centroid).
100
Potential Reductions in Cancer Burden
Population prevention fractions (PPF) can be used in cancer control to compare cancer risk for
populations under current and counterfactual exposure scenarios.
264
PPF can thus quantify the
potential improvement in disease incidence which could result from alternative exposure
scenarios, such as through the implementation of interventions which improve HPV vaccination.
PPFs are calculated by subtracting the incidence rate under a counterfactual exposure to the
baseline incidence rate (I B – IC).
To estimate potential reductions in population level cervical cancer burden by locating
interventions to improve adolescent HPV vaccination in our identified high-risk Latino areas, we
used the following criteria:
- Cervical Cancer Incidence. Age-adjusted incidence rates were calculated for both
geographic areas (high risk Latino vs. elsewhere) using incidence data from the LA
SEER (Los Angeles Cancer Surveillance Program) for years 2006-2019; population
interpolations and extrapolation of the female population based on 2000 and 2010 US
Decennial Census estimates; and the 2010 US Decennial Census as our standard
population (results of the 2020 Decennial Census are not yet available at the ZIP-Code
Tabulation Area).
- Cases Prevented: To calculate cervical cancer cases prevented through HPV
vaccination, we used a number needed to vaccinate (NNV) of 120, per Cataldi and
colleagues;
12
this is an estimate of how many individuals need to be vaccinated against
HPV to prevent one case of cervical cancer.
265
We calculated the number vaccinated
(NV) in both geographic areas based on the population eligible for adolescent HPV
vaccination (9-18 year old’s, for consistency with the CAIR immunization data), current
CAIR estimates of HPV vaccination, and counterfactual vaccination rates in both areas.
101
Cases of cervical cancer prevented were estimated by NVB/NNV – NVC/NNV
(B=baseline, C=counterfactual).
- Counterfactual Risk Reduction. Multimodal and multilevel interventions which
simultaneously address various audiences (parents, adolescents, clinicians, clinic staff,
etc.), behaviors (patient education, staff training, changes to healthcare delivery
practices, etc.), and/or levels of influence (individual, clinic, societal) related to HPV
vaccination behavior have been identified as being effective strategies to improve
adolescent HPV vaccination.
118,3
Informed by the results of dissertation Study 2 which
identified provider recommendations of HPV vaccination as the most impactful predictor
of adolescent HPV vaccination among Latinos residing in a community at high risk for
cervical cancer, we selected our counterfactual risk reduction based on the effectiveness
of multimodal interventions which included a component focused on improving provider
recommendations of the HPV vaccine. To increase comparability to the population
receiving services at our selected clinics, we limited our consideration to interventions
whose participants included male and female adolescents (rather than those focusing on
only one sex, those implemented before public funding was available for both sexes, or
those focused on adults) and public insurance recipients, as well as to interventions
which were not implemented at clinics with high baseline HPV vaccination rates. Based
on a review of the literature,
107,118,211,266
we identified HPV vaccine initiation
improvements ranging from 13%-18% among such interventions.
111,220,266
We selected a
13% improvement in vaccine uptake as our counterfactual scenario to use the most
conservative estimate of the potential improvement that an effective intervention
targeting male and female adolescents including a provider recommendation component
could have in improving HPV vaccine series initiation.
102
RESULTS
Area Characteristics
Utilizing the results of the Kernel Density Analysis described in Study 1, we identified 197
ZCTAs which intersected a cervical cancer hot spot. There were 73 ZCTAs with over 60% of
Latino populations in LAC. In these Latino ZCTAs, we identified 9 which had HPV vaccination
rates below the county average and intersected with a cervical cancer hot spot. Demographic
and variable distributions for these geographic groupings appear on Table 17.
Table 17. Characteristics of Los Angeles County ZCTAs, ZCTAs with >60% Latino populations,
and ZCTAs with >60% Latino populations at high-risk for cervical cancer.
Mean (SD) Mean (SD) Mean (SD)
LAC ZCTAs
(N=277)
Over 60%
Latino
(N=73)
Below 60%
Latino
(N=204) p-value
High Risk
Latino
(N=9)
Not High-Risk
Latino
(N=268) p-value
HPV Rate 0.051 (0.018) 0.062 (0.010) 0.047 (0.018) <0.001 0.047 (0.002) 0.051 (0.018) 0.376
Segregation 0.08 (0.21) -0.09 (0.13) 0.14 (0.20) <0.001 -0.04 (0.13) 0.09 (0.2) 0.054
% Latino 40.93 (25.78) 76.3 (11.1) 28.3 (15.8) <0.001 73.4 (8.2) 39.8 (25.5) <0.001
% Non-US Born 31.93 (12.01) 37.0 (8.8) 30.1 (12.5) <0.001 42.6 (6.0) 31.6 (12.0) 0.003
Tdap Rate 0.061 (0.021) 0.07 (0.01) 0.06 (0.02) <0.001 0.054 (0.005) 0.061 (0.209) 0.192
% Uninsured 8.47 (4.74) 12.9 (4.4) 6.9 (3.7) <0.001 11.8 (2.5) 8.4 (4.8) 0.008
% Public Insurance 36.3 (10.9) 46.4 (8.5) 32.7 (9.2) <0.001 47.0 (6.4) 36.0 (10.8) 0.002
% Below FPL 13.77 (7.9) 19.1 (8.1) 11.8 (6.9) <0.001 16.3 (5.7) 13.7 (8.0) 0.115
All CC* Cases 21.32 (15.27) 31.8 (17.9) 17.6 (12.2) <0.001 31.2 (15.2) 21.0 (15.2) 0.033
LS* CC Cases 11.81 (9.3) 18.1 (11.0) 9.6 (7.4) <0.001 17.7 (6.2) 11.6 (9.3) 0.016
*CC= cervical cancer; LS= late stage
We found that ZCTAs with Latino populations higher than 60% were significantly more likely
than those with smaller populations of Latino residents to have higher HPV and Tdap vaccine
initiation rates (0.06 vs. 0.05, p<0.001, and 0.07 vs. 0.06, p<0.001 respectively), and to have
larger populations of non-US born (37% vs 30%, p<0.001), uninsured (13% vs 7%, p<0.0001),
and publicly insured individuals (46% vs 33%, p<0.001). These areas were also more likely to
experience more disadvantaged residential segregation (-0.09 vs. 0.14, p<0.001) and to have
larger populations residing below the Federal Poverty Level (19% vs. 12%, p<0.001). ZCTAs
with large Latino populations also had significantly more cases of cervical cancer diagnosed
103
between 2006-2019, including cases diagnosed at all stages (32% vs. 18%, p<0.001) and late-
stage cases (18% vs. 10%, p<0.001).
Latino ZCTAs at high risk of cervical cancer (N=9) displayed similar trends in terms of non-US
born, uninsured, and publicly insured populations, as well as in terms of all-stage cervical
cancer incidence burden (see Table 1). HPV and Tdap vaccine initiation rates were lower in
these communities than in the remaining LAC ZCTAs, but this trend was not statistically
significant. (0.047 vs. 0.051, p=0.376, and 0.054 vs. 0.061, p=0.192, respectively).
Of the 200 clinics listed as participants in the Vaccines for Children program in Los Angeles
County, 17 (8.5%) were situated within the 9 identified ZCTAs, constituting our MCDA analytic
sample.
MCDA – Components and Final Score
PCA of Area-level Predictors of HPV Vaccination
We explored the results of PCA on all variables significantly associated with ZCTA-level
adolescent HPV vaccine uptake in bivariate analyses in Study 1: percent of the population in
poverty; percent of Latino population; percent of non-US born population; percent of population
with no health insurance; income segregation; and yearly rate of Tdap uptake.
One factor was extracted in the PCA result; the eigenvalue of the this first factor was 3.80 (for
comparison, the eigenvalue of the second factor was 0.94). Standardized factor scores were
calculated by obtaining standardized scoring coefficient for each variable; these were multiplied
by item responses, and products were summed for a final factor score. A factor score was
calculated for each eligible clinic based on the data from the ZCTA in which the clinic was
situated and included as a variable in the MCDA ranking. The full list of factor patterns,
104
communality estimates, and standardized scoring coefficients for each variable appear listed in
Table 18.
Table 18. Factor pattern and communality estimates for Factor 1 from PCA .
Variable
Factor
Pattern
h
2
Scoring
Coefficient
Percent Latino 0.76 0.57 0.20
Percent Foreign Born 0.59 0.34 0.15
Yearly Tdap Rate 0.63 0.39 0.16
Percent Uninsured 0.90 0.82 0.24
Percent below FPL 0.89 0.79 0.23
Residential Segregation -0.94 0.88 -0.25
h
2
=Communality estimates
Clinic Strategies to Improve Provider Recommendation of HPV Vaccine
We searched public listings to obtain contact information for the 17 VFC clinics which met our
eligibility criteria for study inclusion. Of these, 5 had no current information listed or had
numbers which had been disconnected. 1 additional clinic was closed, and 1 did not offer
vaccination services to individuals ages 9-17. Each of the remaining 10 clinic was contacted a
maximum of three times. 2 clinics declined to participate in the study, 1 no longer participated in
the VFC program, and 1 reported no interventions in place to improve HPV vaccination. We
were unable to contact a representative in the remaining 6 clinics despite several attempts.
Given the poor response rate to our phone survey, we excluded data about clinic strategies to
improve provider recommendation of the HPV vaccine from our MCDA.
HPV Vaccination Rate
Adolescent HPV vaccine initiation rates ranged from 4.4% to 5.1% in the ZCTAs in which the
eligible clinics were located. Rates were subtracted from 0.051 (the maximum rate in the range)
to inverse the direction of the values and obtain higher values for ZCTAs with lower HPV
105
vaccine initiation rates, which would make the clinics located in those areas more suitable for
HPV vaccine interventions.
Cervical Cancer Burden
Eligible clinics were located from 0 to 1585 meters from their nearest cervical cancer hot spot.
We considered that clinics closer to cervical cancer hot spots have populations more vulnerable
to cervical cancer, so the distance measure was subtracted from 1585 (the maximum distance
in the range) to reverse its value and ensure that clinics closer to hot spots ranked higher,
denoting better suitability to implement an intervention to improve HPV vaccination. Percentage
of cervical cancer cases in LAC included in the selected ZCTAs ranged from 0.3-0.9%, and the
proportion of late-stage cases among cervical cancer cases in each ZCTAs ranged from 46.2-
83.3. In one case, ZCTA level cervical cancer frequencies were suppressed in line with CSP
confidentiality standards, which require suppression of geographies with case counts lower than
11. The proportion of the ZCTA included in the nearest cervical cancer hot spot ranged from 5-
42%.
MCDA Final Score
After adding all components, MCDA scores ranged from 61-1668, with higher scores denoting
better suitability for an HPV vaccine intervention. While these MCDA scores do not have
absolute value in themselves, they are important tools for the quantitative comparisons of clinics
with most potential for population-level improvements in HPV vaccine uptake. Of the clinics
included in our analysis, the highest-ranking clinic was Sunkist Multispecialty Medical Clinic in
La Puente, CA (ZCTA 91746), with a MCDA score of 1668.
106
Population Preventable Fraction
The baseline AAIR for the high-risk Latino areas during years 2006-2019 was 8.54, and the
AAIR for non-high-risk, non-Latino areas was 7.99 during the same time period. Baseline HPV
vaccination rate for high-risk Latino areas was 0.047 and 0.051 for the rest of LAC;
counterfactual rates for these areas were 0.053 and 0.058, respectively. Incidence rates using
counterfactual vaccination rates were 5.16 for the high-risk Latino areas and 5.30 for the rest of
the county.
The PPF for high-risk Latino areas was 0.87, and 0.66 in the rest of LAC; the percent change in
the proportion of cervical cancer cases prevented in women resulting from implementing an
intervention to improve adolescent HPV vaccine initiation among high-risk Latino communities
(compared to the rest of the county) was 31%.
Dissemination of Study Results
We used the ArcGIS Online Dashboard application to create an online visualization platform
that could be used to disseminate our results. We identified our dashboard audience as
incorporating all stakeholders engaged in strategies to improve HPV vaccination, including
community leaders, practitioners, academics, and policy makers. The publicly available
“Optimizing Adolescent HPV Vaccination at LA County Latino Communities at High Risk for
Cervical Cancer” ArcGIS Online Dashboard
(https://www.arcgis.com/apps/dashboards/99daa4dc461e4fe8ab00248a1944acec) displays all
17 VFC clinics located within the high-risk Latino areas, with an accompanying pop-up window
which displays clinic information (name, address), clinic rankings, and total clinic MCDA score
as well as further information about all variables used in the MCDA score calculations, in
addition to HPV vaccine initiation rates for the ZCTA in which each clinic is situated and the
percent of the ZCTA overlapping with a cervical cancer hot spot. (see Figure 16). Our map also
107
includes the location of the high-risk Latino ZCTAs and cervical cancer hot spots across Los
Angeles County. A text panel briefly describes the aim of the dashboard, the map contents, and
provides a simple explanation of the ranking criteria. Data sources and author contact
information are also included.
Figure 16. Screenshot of the “Optimizing Adolescent HPV Vaccination at LA County Latino
Communities at High Risk for Cervical Cancer” online dashboard.
DISCUSSION
The MCDA analysis showed a wide range of scores in the 17 clinics considered in our analysis
(61-1668). While these numbers do not have absolute values in themselves, they do show that
factors associated with cervical cancer burden vary broadly even in high-risk Latino
communities. We observed small variations in HPV vaccine uptake (4.4% to 5.1%) in the
selected areas, but a large variation in cervical cancer vulnerability in terms of distance of these
108
clinics from their nearest cervical cancer hot spot (0 to 1585 meters) and proportion of late-
stage cervical cancer cases in the ZCTA where the clinics are located (46.2 to 83.3). The values
for proportion of cervical cancer cases diagnosed at a late stage among the ZCTAs in our
sample is especially striking in terms of both magnitude and range, and seems to affirm national
patters of higher cervical cancer cases diagnosed at late stages among Latinas.
5,6,13
Healthcare
availability and cultural norms surrounding cervical cancer screening and HPV vaccination in
these communities could be associated with this trend. Using the Theory of Planned Behavior
158
as a guide to understand screening and vaccination behavior among Latinas, social norms have
been identified to impact cervical cancer screening intentions and HPV vaccination.
155,267,268
Our
findings highlight a need for deeper exploration of social norms, access to, and uptake of
cervical cancer screening services in these communities.
Consistent with the literature,
234,236,238
we found that ZCTAs in LAC with large Latino populations
had higher uninsurance rates. We also found that these geographies were more likely to have
higher proportions of residents with public insurance, validating our decision to focus on VFC
clinics as our unit of analysis. Of note, while we found that Tdap uptake was higher in Latino
communities overall, we found that uptake of Tdap was lower in Latino communities at high risk
for cervical cancer, though this was not statistically significant. This trend is worth exploring
further, as the lack of statistical significance could be a reflection of the small sample size of
high-risk Latino geographies (N=9) in our study. As HPV vaccination below the county average
was one of the defining characteristics of these high-risk areas, if true this pattern could reflect
underlying negative community attitudes towards adolescent vaccinations more broadly or
limited availability of vaccination providers in these neighborhoods.
102
Response rates for our phone survey were very low, such that we were unable to include
information about strategies in place to improve HPV vaccination rates at the clinics included in
109
our analysis. While this limits the interpretability of our results, it is perhaps not surprising that
clinics located in areas with low vaccine uptake have limited resources to speak to a researcher
and participate in data collection activities which would detract from providing care in a
resource-constricted setting. Of concern, this could reflect limitations to the quality and
availability of resources provided at these clinics, which could be an important determinant of
vaccination uptake in these communities. As our data collection efforts took during the winter of
2022-2023, it is possible that some health centers were overwhelmed as they try to catch up on
preventive care services delayed during the pandemic lockdowns.
269,270
As an accurate
assessment of the existence, availability, and quality of practices in place to improve HPV
vaccination in these areas is important for efforts to reduce cervical cancer incidence in
vulnerable Latino communities, further research should explore more effective strategies for
engaging clinic stakeholders in these communities in data collection activities.
We found that locating an intervention to improve HPV vaccine uptake in Latino areas at high
risk for cervical cancer could lead to reductions of cervical cancer incidence over 31% greater
than locating these interventions in other areas of the Los Angeles County. These results
highlight the importance of identifying areas most at risk for cervical cancer incidence, and of
situating interventions at locations where populations most at risk receive care.
Utilizing the results of our MCDA analysis, we developed a publicly available online dashboard
which provides users with a quantitative ranking of the 17 VFC clinics located in Latino
communities at high risk of cervical cancer based on cervical cancer burden, HPV vaccination
rates, and sociodemographic factors correlated with area-level HPV vaccine uptake. Our
dashboard also visualized the distribution of cervical cancer hot spots in LAC, and detailed pop-
ups for all VFC clinics provided further information on variables used for rank scoring. Further
research should focus on conducting a more formal analysis of whether GIS-based, public, and
110
free online dashboards can be an effective dissemination strategy among HPV vaccination
stakeholders.
Several limitations to this research should be noted. As previously mentioned, we were unable
to include information about clinic strategies in place to improve HPV vaccine uptake, limiting
the interpretability of our ranking scores. While our study incorporated data from multiple local
sources to provide information on optimizing prevention strategies at local clinics, our results are
not generalizable outside of our selected sites, though our process can be replicated elsewhere.
Moreover, since we are only focusing on communities with over 60% percentage of Latino
residents, our dashboard does not provide information on how to optimize prevention
interventions in other racial/ethnic communities, nor the ability to compare clinics in high-risk
with those in low-risk areas. Lastly, our dashboard does not include processes for automatic
updates based on the availability of new data, so the accuracy of the information presented is
limited to the denoted time frames.
However, our study provides a promising first step in developing an approach which can support
quantitative comparisons and help identify the best places to intervene for population-level
improvements in HPV vaccination and cervical cancer burden. Furthermore, the results of this
study can guide the strategic targeting of intervention resources to locations with most the
potential for reducing cancer rates and addressing HPV-related disparities, within the realities of
conflicting priorities and limited resources. Further research should expand our approach to
other populations and geographies beyond Los Angeles County.
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CHAPTER 6: Discussion, Implications and Future Directions for HPV Vaccination Among
Diverse Latino Communities.
SUMMARY OF FINDINGS
This dissertation explored how factors operating at the individual, interpersonal, and community
levels of the Social Ecological Model impact HPV vaccine uptake among Latino adolescents in
Los Angeles County. Specifically, the studies aimed to (1) identify spatial patterns in HPV
vaccination in Los Angeles County and explore the area-level factors impacting HPV
vaccination across Los Angeles County communities, (2) identify the personal and interpersonal
factors impacting HPV vaccination among Latinos residing in a community at high-risk for
cervical cancer, and (3) identify optimal Latino communities at high-risk for cervical cancer in
which to implement an intervention to improve HPV vaccination.
Study 1 found that HPV vaccination uptake among adolescents in Los Angeles County varied
broadly, and that the average rate of uptake in the County using CAIR estimates was well below
national estimates of HPV vaccination uptake. We found that geographic weighted regression
models performed better in estimating the factors impacting HPV vaccination in Los Angeles
County ZCTAs than ordinary least squares models. The analyses identified ZCTA level Tdap
vaccine uptake as the strongest positive correlate of HPV vaccination. Furthermore, these
models highlighted that adolescent HPV vaccination was positively associated with ZCTA-level
nativity, Latino ethnicity, and insurance in some Los Angeles County ZCTAs, while being
negatively associated with them in other areas. These findings highlight the importance of using
spatial regression models that account for spatial autocorrelation and that does not assume a
static relationship between predictors and outcome across the study area. In addition, Study 1
found a positive relationship between adolescent HPV vaccination and cervical cancer clusters
in Los Angeles County.
112
Study 2 identified that lack of a provider recommendation for the HPV vaccine and male
parental/caregiver sex were negatively associated with HPV vaccine uptake among parents of
Latino adolescents after controlling for controlling for HPV vaccine awareness, HPV vaccine
hesitancy, adolescent Tdap uptake, and adolescent gender. We also found that parental
acculturation significantly modified the relationship between provider recommendations and
adolescent HPV vaccination, and that the positive impact of a provider recommendation to
vaccinate on HPV vaccine uptake is more pronounced among high acculturated Latino parents.
This underscores the importance of exploring factors impacting adolescent HPV vaccination in
different Latino sub-groups and of designing interventions that are responsive to these sub-
group variations.
Study three used a implemented a MCDA to integrate data on HPV vaccination and cervical
cancer burden and create a score that allows for quantitative comparisons among VFC clinics
located in high-risk Latino ZCTAs, in terms of suitability of implementing an intervention to
improve HPV vaccination that can reduce population-level cervical cancer burden. The MCDA
scores analysis in the 17 clinics within the identified ZCTAs ranged between 61 and1668, with
the largest variation present in distance from the clinics to the nearest cervical cancer hot spot,
and proportion of late stage cases of cervical cancer in the ZCTA where the clinic was located.
Population preventable fractions showed that implementing an intervention to improve HPV
vaccination in clinics located within these communities would have a 26% larger reduction in
cervical cancer incidence than locating the intervention in clinics outside the selected ZCTAs.
As a first step in disseminating our study results, we utilized a publicly available GIS-based
online dashboard to visualize our findings.
113
IMPLICATIONS
All three of the studies in this dissertation highlight the importance of acquiring more a more
granular understanding of Latino communities in terms of sub-populations, geographies in which
they reside, and risk level in terms of identifying their behavioral risk factors in more accurate
ways. Our results highlight the need to develop interventions based on such a granular
understanding of the needs of these communities, based on a more complete knowledge of the
factors impacting HPV vaccine behavior beyond averages calculated at a county or population
level.
In large urban centers, such as the County of Los Angeles, it is important for the effective
allocation of limited resources that we identify and prioritize the areas with greatest need, and
that we explore the factors which underlie such need in diverse communities. Our results
suggest that implementing one-size-fits-all interventions informed by relationships observed at
county or population level averages may be insufficient to improve adolescent HPV vaccination
among vulnerable Latino groups, and addressing disparities in cervical cancer incidence among
Latinas. While great progress has been accomplished in designing culturally and language
appropriate interventions, the results of this dissertation suggest we need to understand the
communities we serve more deeply, and to more explicitly acknowledge the diversity present in
them in terms of beliefs, preferences, and patterns of health behavior. Our results provide a first
step in identifying which communities should be explored further, but additional research is
needed to understand the relationships that this dissertation has uncovered.
More specifically, our results suggest that interventions focused on improving adolescent HPV
vaccination by targeting individual and interpersonal-level factors among high acculturated
Latinos would benefit from implementing interventions to improve provider recommendations of
the HPV vaccine to parents in this group. Similarly, our results suggest that at an area-level,
114
identifying ways to increase to co-administration of HPV and Tdap vaccines can bring about
increases in adolescent HPV vaccination across Los Angeles County. These findings can be
important for community stakeholders and policymakers interested in improving HPV
vaccination within the context of constrained resources and competing priorities.
Furthermore, the results of Study 3 highlight the value of implementing such interventions in
areas of most cervical cancer vulnerability, especially among communities with large Latino
populations, low HPV vaccination rates, and high cervical cancer incidence and density. Our
results suggest that this targeted location of interventions can provide greater improvements in
cervical cancer incidence reductions that generalized or convenience-based approaches for
identifying where to implement interventions to improve adolescent HPV vaccination.
Moreover, the use of GIS in studies 1 and 3 helped us to better pinpoint and characterize some
of the geographic disparities identified in this dissertation research. Additionally, our use of GIS
provided guidance on how to begin exploring the causes of the disparities observed (for
example, when low HPV vaccination rates are identified in areas of low provider availability) and
can help us identify the areas of most need in which resource allocation and research efforts
should be prioritized.
OVERALL DISSERTATION LIMITATIONS
There are various issues with HPV disease reporting and HPV vaccination data that present
limitations for our studies. HPV is not a mandated reportable disease,
1
so exact assessment of
HPV infection prevalence and incidence are unknown. While we know HPV infection is widely
present in the population at large, we do not know about disparities in HPV infection that may be
placing several populations at additional risk.
115
Overall low HPV vaccine uptake in some geographies also creates challenges for obtaining and
analyzing disaggregated sub-county data. CAIR confidentiality standards dictate that
geographies containing less than 11 vaccinated individuals be suppressed, creating missing
data and obfuscating our understanding of the factors impacting HPV vaccine uptake in
geographies with less than 11 individuals vaccinated, which could be especially vulnerable to
HPV-associated cancers. Such standards also made impossible to obtain data disaggregated
by racial/ethnic group, which would have provided important insights on disparities in HPV
vaccine uptake. Additionally, CAIR reporting is not currently mandated for all providers, limiting
the number of vaccinations which are captured in the registry.
Furthermore, the studies described in this proposal do not incorporate data on cervical cancer
screening or healthcare service accessibility, which are important considerations in determining
overall risk of cervical cancer.
All dissertation studies propose cross-sectional analyses and do not incorporate a time
component. Examining how the timing of the changing ACIP guidelines regarding HPV vaccine
eligibility impacted HPV vaccine uptake and potentially modified some area-based relationship
with our predictors of interest.
Additionally, our research focuses on populations residing in Los Angeles County, a large urban
center within a liberal state with substantial health subsidies, among other policies which would
impact HPV vaccination uptake among Latino adolescents.
151,152
The patterns observed in our
results could change greatly among smaller, less heterogeneous populations; among
metropolitan centers with smaller Latino communities; and within counties states with limited
support for healthcare service delivery.
116
Another limitation of this dissertation is the lack of comparison groups. Additionally, as much of
this research highlighted the importance in understanding variability in Latino sub-groups and
sub-county geographies, relatively small sample sizes impacted the robustness of our statistical
results, especially in the models which disaggregated data to explore sub-group trends.
Despite these limitations, the results of the proposed studies improve our understanding of the
factors impacting HPV vaccine uptake among vulnerable communities in Los Angeles County,
especially among Latinos residing in areas with low HPV vaccination and high cervical cancer
incidence.
FUTURE RESEARCH DIRECTIONS
The results of this dissertation research point to a few important avenues of future research to
improve our understanding of adolescent HPV vaccination among vulnerable Latino
communities.
Our research should be replicated in larger Latino samples with varied acculturation levels.
Furthermore, such research should be conducted in different Latino communities and include
non-Latino comparison samples, to address some of the limitations identified in this dissertation.
Future research should focus on identifying correlates of area-level HPV vaccination using other
geographic boundaries, especially census tracts which are more informative boundaries in
terms of population measures and are less likely to change over time.
271
More research to explore the perspectives of provider and clinic staff providing vaccination
services in vulnerable communities is also needed. In particular, we should focus on
understanding provider perspectives on HPV vaccine recommendation practices among parents
117
of Latino adolescents, and on the competing priorities facing the practices and clinics serving
Latino adolescents in areas at high risk.
Lastly, we need to obtain more data which can explain some of the area-based variations
identified through this dissertation. Focusing on collecting data on the factors impacting HPV
vaccination behavior in some of the identified geographies can help us design interventions that
address the needs and preferences of the communities most impacted by cervical cancer
burden, and address the cervical cancer health disparities facing Latino communities in Los
Angeles County.
118
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APPENDIX 1. Los Angeles County neighborhoods with overlap with high-risk areas.
Los Angeles Neighborhood % Overlap
Vincent 1.06
Montebello 1.24
Artesia 1.47
Beverly Crest 2.15
Palms 2.27
Ramona 2.68
Hacienda Heights 3.17
Northridge 3.57
Playa del Rey 4.17
Harbor City 4.49
Cypress Park 5.16
North Hollywood 5.43
Glassell Park 6.12
Larchmont 6.24
Van Nuys 6.94
Del Aire 9.35
Sherman Oaks 9.78
Echo Park 10.00
Mid-City 11.22
Wilmington 11.34
Diamond Bar 13.46
Tujunga Canyons 17.25
Lake View Terrace 17.49
Beverly Grove 17.58
Bel-Air 18.21
Studio City 18.39
Sepulveda Basin 19.20
East Hollywood 21.78
Hansen Dam 25.30
Pasadena 27.47
Beverly Hills 29.06
Shadow Hills 30.55
Century City 32.71
Hancock Park 35.78
Long Beach 36.21
Mid-Wilshire 37.29
West Los Angeles 37.90
Encino 42.47
Veterans Administration 44.05
Pomona 44.32
141
Sawtelle 46.74
Beverlywood 47.52
Silver Lake 48.17
Valley Glen 51.74
Carthay 51.82
Redondo Beach 56.27
Hollywood 57.92
Monrovia 58.57
Burbank 59.45
Elysian Valley 59.79
Glendale 61.30
Avocado Heights 61.49
Mayflower Village 71.88
Torrance 76.13
Industry 78.04
Irwindale 78.79
Eagle Rock 84.06
Toluca Lake 84.20
West Hollywood 84.29
Westwood 84.95
Claremont 85.02
Brentwood 85.85
Valley Village 85.94
Tarzana 89.54
Altadena 89.84
Whittier Narrows 90.65
Tujunga 93.49
Cheviot Hills 94.96
San Pedro 96.06
Rowland Heights 96.69
Westchester 96.87
Rolling Hills 97.06
Rolling Hills Estates 97.51
Hawaiian Gardens 97.64
Cerritos 97.77
Walnut 98.12
Rosemead 98.53
Lomita 99.11
Sunland 99.12
Hollywood Hills 99.18
Lakewood 99.19
Manhattan Beach 99.24
South El Monte 99.39
142
West Covina 99.45
Fairfax 99.49
Monterey Park 99.58
Hollywood Hills West 99.76
Palos Verdes Estates 99.81
San Gabriel 99.88
Alhambra 99.88
Griffith Park 99.91
South San Gabriel 99.93
Atwater Village 99.93
Los Feliz 99.93
East San Gabriel 99.93
San Pasqual 99.95
El Monte 99.97
South San Jose Hills 100.00
Pico-Robertson 100.00
Temple City 100.00
Rancho Park 100.00
Arcadia 100.00
Baldwin Park 100.00
La Puente 100.00
Valinda 100.00
East Pasadena 100.00
West Puente Valley 100.00
North El Monte 100.00
143
APPENDIX 2. Study 3 Questionnaire with Interviewer and Coder Instructions
Thank you for taking your time to talk to me today. I’m going to ask you a few questions about the
programs or initiatives that your clinic/practice has in place to improve HPV vaccination, if any. There are
no right or wrong answers to these questions; I am trying to understand what services are being provided
at your clinic/practice, so you are the expert on this topic. The questions will take approximately 10
minutes to complete. If at any point a question makes you feel uncomfortable, you can skip it or refuse to
answer it. Before we begin, I want to confirm you are the right person to ask these questions at your
organization.
SCREENER QUESTION: Do you know about the strategies or initiatives implemented at your
clinic/practice to improve HPV vaccination rates over the past 6 months?
[If yes, proceed with questionnaire. If not, inquire about the appropriate person to complete the
questionnaire.]
1. What is your role at the clinic/practice?
2. How long have you been at your current role?
In the past six months, has your practice/clinic:
Yes
(1)
No
(2)
Don’t
know
(5)
Refused
to
answer
(6)
3. Encouraged providers to routinely recommend the HPV
vaccine to children 11 to 12 years old?
IF YES:
- a. How frequently are providers encouraged to recommend the HPV vaccine?
- b. Which staff member(s) is responsible for making the recommendation?
- c. Are there incentives offered to providers who recommend the HPV vaccine?
- d. Who is responsible for encouraging providers to recommend the HPV vaccine?
- e. Are providers encouraged to recommend the HPV vaccine to boys, girls, or both?
- f. A. Are there Spanish-speaking providers in your practice?
- f. B. Are there Spanish translators available at your practice?
- f. C. Are the recommendations provided in Spanish (for Spanish-speaking parents)?
- g. Do providers know the guidelines for HPV vaccination?
- h. Do your providers receive any training on how to answer parents’ questions about the
HPV vaccine?
4. a. Are patient records flagged to remind providers of need to
recommend HPV vaccination?
b. Are Electronic Health Record alerts turned on?
c. Does staff routinely take action on the alerts to recommend
the HPV vaccine?
d. Any other provider prompts to recommend the HPV
vaccine in place?
5. Provided individualized reports to clinicians about their HPV
immunization data?
6. During the last six months, have there been any other programs or quality improvement
initiatives to increase HPV vaccination rates at your practice/clinic?
[IF YES]: Can you tell me what they are?
7. Do you think the initiatives implemented at the clinic/practice actually helped to improve
adolescent HPV vaccination rates over the past 6 months?
That is the end of my questions. Thank you so much for talking to me today.
Coding instructions: Use the numbers indicated below each answer choice as response codes. For
questions with no answer (missing) code “99”. If more than one answer is given for a question, request
clarification from participant. If answer is still ambiguous, code “88”.
Abstract (if available)
Abstract
Introduction: In the United States, Latinas are 43% more likely to be diagnosed with cervical cancer than non-Hispanic white women, and 20% more likely to die as a result, with nearly all cervical cancers attributed to human papillomavirus (HPV) infection. Latinos account for 49% of the population in Los Angeles (LA) County, and data from the 2018 Los Angeles County Health Survey reveal that Latino adolescents in the county have lower vaccination rates than non-Hispanic whites (45% vs. 54%). A more granular, community-centered exploration of the multilevel factors associated with HPV vaccination in Latino communities is needed to understand the strategies necessary to improve the disproportionate cervical cancer burden in this group.
Methods: Geographic weighted regression was used to examine the relationship (including assessing spatial correlation) between ZIP code tabulation area (ZCTA) level factors (i.e., poverty, uninsurance, nativity, Latino ethnicity, Tdap uptake, residential segregation) and ZCTA level HPV vaccine uptake (from the California Immunization Registry) among adolescents (ages 9-17) residing in Los Angeles County; areas of the county within a hotspot and with low HPV vaccination rates were determined to be at high risk for cervical cancer (Study 1). Multivariable logistic regression was used to identify the personal (e.g., acculturation, knowledge) and interpersonal (e.g., medical mistrust, provider recommendation) factors impacting HPV vaccine uptake among Latino parents of adolescents residing in a community with high cervical cancer incidence and low HPV vaccine uptake; we also explored how these varied by acculturation level (Study 2). Finally, GIS-based Multi-Criteria Decision Analysis (MCDA) was used to incorporate both community, interpersonal, and individual level factors to identify clinics in Latino communities with largest potential for HPV vaccination uptake improvements; a population preventable fraction quantified the improvements in cervical cancer burden by implementing interventions to improve HPV vaccination in high-risk Latino communities (Study 3).
Results: Study 1 found that HPV vaccination uptake among adolescents in Los Angeles County varied broadly, and that the average rate of uptake in the County using CAIR estimates was well below national estimates. Geographic weighted regression models identified ZCTA-level Tdap vaccine uptake as the strongest positive correlate of HPV vaccination; and found that adolescent HPV vaccination was positively associated with ZCTA-level nativity, Latino ethnicity, and insurance in some Los Angeles County ZCTAs, while being negatively associated with them in other areas. Study 2 found that lack of a provider recommendation for the HPV vaccine and male parental/caregiver sex were negatively associated with HPV vaccine uptake among parents of Latino adolescents residing in a community at high risk for cervical cancer, after controlling for all other predictors in the model. We also found that parental acculturation significantly modified the relationship between provider recommendations and adolescent HPV vaccination, and that the positive impact of a provider recommendation to vaccinate on HPV vaccine uptake was more pronounced among high acculturated Latino parents. Study 3 identified 17 VFC clinics located in high-risk Latino communities in Los Angeles County, and found that MCDA scores ranged between 61 and 1668. The largest variation in the component scores were distance from the clinics to the nearest cervical cancer hot spot, and proportion of late-stage cases of cervical cancer in the ZCTA where the clinic was located. Population preventable fractions found reductions in cervical cancer incidence 31% greater resulting from implementing an intervention to improve HPV vaccination in clinics located within these communities, compared to locating them in clinics outside the selected ZCTAs. Lastly, we utilized a publicly available GIS-based online dashboard to visualize our findings as a first step in disseminating our study results.
Conclusion: The exploration of multilevel factors associated with HPV vaccine uptake in vulnerable communities is critical to identifying actionable approaches for improving HPV vaccination in populations most in need for long-term cervical cancer prevention strategies and decrease the disproportionate burden of HPV-associated cancers among Latinos.
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Asset Metadata
Creator
Martinez, Bibiana M.
(author)
Core Title
Exploring geography and multi-level factors associated with disparities in HPV vaccination among Latino adolescents in Los Angeles County
School
Keck School of Medicine
Degree
Doctor of Philosophy
Degree Program
Preventive Medicine
Degree Conferral Date
2023-05
Publication Date
09/29/2024
Defense Date
03/29/2023
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
cancer prevention,disparities,HPV vaccination,Latinos,OAI-PMH Harvest
Format
theses
(aat)
Language
English
Contributor
Electronically uploaded by the author
(provenance)
Advisor
Cockburn, Myles (
committee chair
), Baezconde-Garbanati, Lourdes (
committee member
), Palinkas, Lawrence (
committee member
), Pickering, Trevor A. (
committee member
), Tsui, Jennifer (
committee member
)
Creator Email
bibianam@usc.edu
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https://doi.org/10.25549/usctheses-oUC112850379
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UC112850379
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etd-MartinezBi-11538.pdf (filename)
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etd-MartinezBi-11538
Document Type
Dissertation
Format
theses (aat)
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Martinez, Bibiana M.
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texts
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20230330-usctheses-batch-1013
(batch),
University of Southern California
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University of Southern California Dissertations and Theses
(collection)
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Tags
cancer prevention
disparities
HPV vaccination