Assessment of Clustering of Kindergarteners Not-Up-To-Date on Vaccines After Elimination of Personal Belief Exemptions in California Open Access

Abstract

In 2015, California implemented the most stringent new vaccination policy passed in more than 30 years, known as California Senate Bill 277 (SB277). This new law eliminated the option of a personal belief exemption to the mandated immunization requirements for entry to private and public schools. Prior research on the impact of SB277 has focused on the overall rates of vaccine exemptions in the state with little focus on the potential changes in spatial heterogeneity of kindergarteners who are not-up-to-date on their vaccines.This is the first study to examine the impact of SB277 on the clustering of and exposure to kindergartners who are not-up-to-date on their vaccines. Using data from the California Department of Public Health from 2000 to 2017 we assessed the clustering and spatial heterogeneity of not-up-to-date kindergartners. We also calculated two state-level measures of likelihood of exposure to not-up-to-date kindergarteners among other kindergartners: the aggregation index and the interaction index. The interaction index measures the probability of contact between a kindergartener who is up-to-date and a kindergartner who is not-up-to-date on their vaccines within the state, while the aggregation index measures the probability of contact between two not-up-to-date kindergarteners. The interaction index peaked at 8.23 in 2013 and fell to 1.35 two years after SB277 was implemented. Similarly, the aggregation index peaked at 27.09 in 2014 and fell to 8.94 in 2017. Our spatial analyses also indicated a reduction in the spatial clustering of not-up-to-date kindergartners, and decreasing not-up-to-date rates for many areas of the state after SB277 was implemented. Our results indicate that SB277 has been successful in reducing the clustering and exposure to kindergartners who are not-up-to-date on their vaccines in California. Reducing the aggregation and clustering of kindergartners who are not up-to-date on their vaccines helps to minimize the likelihood of disease outbreaks due to low vaccination coverage. Other states considering similar legislation can use SB277 as an example of the positive public health impact pro-vaccine legislation can have.     

Table of Contents

Table of Contents 

Introduction...................................................................................................................................... 1

Methods........................................................................................................................................... 3

Data Sources................................................................................................................................ 3

Imputation Data............................................................................................................................ 4

Interaction and Aggregation Indices............................................................................................. 6

Kriging......................................................................................................................................... 8

Clustering Analysis and Quantifying Change in Heterogeneity................................................... 8

Results........................................................................................................................................... 10

Interaction and Aggregation Indices........................................................................................... 10

Kriging....................................................................................................................................... 10

Clustering Analysis and Quantifying Change in Heterogeneity................................................. 11

Discussion..................................................................................................................................... 12

Conclusion..................................................................................................................................... 13

Acknowledgements........................................................................................................................ 14

References...................................................................................................................................... 22

 

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School	Laney Graduate School
Department	Epidemiology
Degree	M.S.
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Epidemiology
Keyword	Vaccines Vaccination SB 277 California
Committee Chair / Thesis Advisor	Saad B Omer, Emory University
Committee Members	Allison Chamberlain, Emory University Walter Orenstein , Emory University

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