Spatial Clustering of Increases in Medical Vaccine Exemptions following California Vaccine Policy Change

• In Event: 2261 - Current Issues in Health Policy

Abstract

Increasing numbers of children entering schools with non-medical vaccine exemptions and increased prevalence of vaccine preventable disease prompted California to pass Senate Bill 277 in 2015, eliminating non-medical exemptions to vaccine requirements for school entry. This prompted a subsequent increase in the percentage of students entering kindergartens with medical exemptions. We use spatial scan statistics on a longitudinal dataset of vaccine exemptions in California kindergartens from 2014-2017 to show that spatial clustering previously exhibited in non-medical exemptions emerges in medical exemptions following the implementation of Senate Bill 277. Furthermore, proximity to clusters of schools with statistically significantly higher rates of non-medical exemptions in 2014 has a positive effect on school-level rates of medical exemptions following the policy change. The emergence of spatial clusters of medical exemptions in areas with previously high non-medical exemption rates may further threaten local herd immunity and increase risk of disease transmission. These results demonstrate that policy changes eliminating non-medical vaccine exemptions may have the unintended consequence of increasing both the rates and spatial concentration of medical exemptions in schools.

Authors

• Ashley Gromis, Princeton University

• Ka-yuet Liu, University of California-Los Angeles