Understanding the impact of state vaccination laws on exemption rates

Measuring Multiple Dimensions and Indices of Nonvaccination Clustering in Michigan, 2008-2018

Michigan experienced a significant measles outbreak in 2019 amidst rising rates of nonmedical vaccine exemptions (NMEs) and low vaccination coverage compared with the rest of the United States. There is a critical need to better understand the landscape of nonvaccination in Michigan to assess the risk of vaccine-preventable disease outbreaks in the state, yet there is no agreed-upon best practice for characterizing spatial clustering of nonvaccination, and numerous clustering metrics are available in the statistical, geographical, and epidemiologic literature. We used school-level data to characterize the spatiotemporal landscape of vaccine exemptions in Michigan for the period 2008-2018 using Moran's I, the isolation index, the modified aggregation index, and the Theil index at 4 spatial scales. We also used nonvaccination thresholds of 5%, 10%, and 20% to assess the bias incurred when aggregating vaccination data. We found that aggregating school-level data to levels commonly used for public reporting can lead to large biases in identifying the number and location of at-risk students and that different clustering metrics yielded variable interpretations of the nonvaccination landscape in Michigan. This study shows the importance of choosing clustering metrics with their mechanistic interpretations in mind, be it large- or fine-scale heterogeneity or between- and within-group contributions to spatial variation.

In the Wake of a Pandemic: Revisiting School Approaches to Nonmedical Exemptions to Mandatory Vaccination in the US

Mandatory school vaccination policies with exclusion of unvaccinated students can be a powerful tool in ensuring high vaccination rates. Some parents may object to mandatory vaccination policies, claiming exemptions based on medical, religious, or philosophical reasons. Individual schools, school systems, or local or regional governments have different policies with respect to whether, and what kind of, exemptions may be allowed. In the setting of the current pandemic, questions regarding the acceptability of exemptions have resurfaced, as schools and local governments struggle with how to safely return children to school. Anticipating that school attendance will be facilitated by the development of a vaccine, school systems will face decisions about whether to mandate vaccination and whether to permit exemptions. The American Academy of Pediatrics promulgates policy favoring the elimination of nonmedical exemptions generally in schools. This discussion considers whether schools should eliminate nonmedical exemptions to vaccination as proposed in the American Academy of Pediatrics policy, ultimately concluding that broad elimination of exemptions is not justified and advocating a more nuanced approach that encourages school attendance while promoting vaccination and broader public health goals.