Neighborhood political composition and personal belief exemptions from immunization requirements in California Kindergartens, 2000-2015.

Introduction: The growing proportion of parents filing personal belief exemptions (PBEs) from school-based vaccine requirements, and the clustering of PBEs in particular schools and communities, could weaken herd immunity and increase vaccine-preventable disease. Alignment of vaccine opposition with a particular political party or ideology could substantially increase PBEs. This study extends our understanding of the link between vaccine refusal and politics by identifying longitudinal associations between neighborhood political composition and school-level prevalence of PBEs between 2000 and 2015 in California.

Methods: California Department of Public Health data on PBEs in kindergartens were matched with political party registration and voting data from the California Statewide Database. Variables for partisan composition and for conservative political ideology, as well as school and neighborhood controls, were used to estimate both mixed-effects and fixed-effects regression models.

Results: PBE rates increased more rapidly in schools located in highly Republican neighborhoods, and were three times higher than PBE rates in highly Democratic neighborhoods in 2013 (6.6% compared to 2.2%). Mixed-effects models predict a 2.3 percentage-point increase in PBEs between 2007 and 2013 for schools in neighborhoods one standard deviation above the mean for % Republican (59%), compared to a 0.8-point increase for schools in neighborhoods one standard deviation below the mean (24% Republican). Similar results were obtained when using a measure of neighborhood conservatism and when models were estimated using fixed effects.

Conclusions: Results indicate growing opposition to mandatory vaccinations in Republican/conservative neighborhoods, which could increase PBE clustering and increase the likelihood for outbreaks of disease in areas where conservative values are widely shared.