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Background:Personal belief exemptions (PBE) from school vaccination requirements have risen in California in the past decade. Outbreaks of measles and varicella in the state have been linked to clusters of intentionally unvaccinated children in schools. Schools with a high prevalence of intentionally unvaccinated children are epidemiologic “hotspots” and should be the focus of policy and programmatic interventions.
Objectives: (1) To calculate the proportion of all kindergarteners in California who attend schools where PBE prevalence exceeds 5% (2) To calculate the proportion of all kindergarteners with PBEs in California who attend schools where PBE prevalence exceeds 5%. (3) To identify school-level and community-level characteristics associated with high PBE prevalence.
Methods: School-level data on PBEs from the California Department of Public Health for 2008 and 2009 were merged with school and community characteristics from the California Department of Education and the US census. The proportion of all kindergarteners attending school with PBE rates > 5% and the proportion of all kindergarteners with one or more PBE attending schools with PBE rates > 5% were calculated. Negative binomial regression was used to estimate the school- and community-level correlates of PBE rates.
Results: In fall 2008, 10% of kindergarteners in California (N=495,884) attended schools where the PBE rate exceeded 5%. For the same year, 61% of kindergarteners with one or more PBEs (N=9,196) attended schools with a PBE rate > 5%. Of those, one-third attended schools where the PBE rate exceeded 20%. The school types most highly associated with PBEs were Waldorf schools (IRR = 28.3) and California Virtual Academy, a homeschooling organization (IRR = 21.4).
Conclusions: More than 50,000 kindergarteners in California attend schools with epidemiologically worrisome rates of PBEs. Policies to limit both the prevalence and clustering of PBEs within schools are needed.