How many California children are exposed to high school-level rates of personal belief exemptions from childhood vaccines?

Introduction: Personal belief exemptions (PBE) from school vaccination requirements have risen in California in the past decade. Disease outbreaks in the state have been linked to clusters of intentionally unvaccinated children. Schools with a high prevalence of intentionally unvaccinated children are epidemiologic “hotspots” and should be the focus of policy and programmatic interventions. The goals of this study were to calculate (1) the proportion of all kindergarteners and (2) the proportion of all kindergarteners with PBEs who attend schools where PBE prevalence exceeds 5%; and to identify school-level and community-level characteristics associated with PBE prevalence. Methods: School-level data on PBEs from the California Department of Public Health were merged with school and community characteristics from the California Department of Education and the US census. The proportion of all kindergarteners and of all kindergarteners with one or more PBEs 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 type most highly associated with PBEs was Waldorf schools. 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.