Getting personal: how childhood vaccination policies shape the landscape of vaccine exemptions

Background: State-mandated school entry immunization requirements in the United States play an important role in achieving high vaccine coverage, but variations in vaccine exemption policies result in a patchwork of vaccine coverage across the country. Methods: In this study, we evaluate epidemiological effects and spatial variations in nonmedical exemption (NME) rates in the context of vaccine policies. We first analyze the correlation between NME rates and vaccine coverage for 3 significant childhood vaccinations. Furthermore, we assess the effects of policy changes in a subset of states, using a correlative approach at the state level and performing a clustering analysis at the county level. Results: We find that higher rates of exemptions are associated with lower vaccination rates of school-aged children in all cases. In a subset of states where exemption policy has recently changed, we show that the effects on statewide NME rates vary widely and that decreases in NMEs can lead to an increase in other types of exemptions. Finally, our clustering analysis in California, Illinois, and Connecticut shows that policy changes affect the spatial distribution of NMEs. Conclusions: Our work suggests that vaccination policies have significant impacts on patterns of herd immunity. Our findings can be used to develop evidence-based vaccine legislation.