Geographic hot spot analysis of vaccine exemption clustering patterns in Michigan from 2008 to 2017.

Objective: This study explored vaccine exemption clustering in Michigan and examined whether vaccine exemptions clustered by exemption type (medical, religious, and philosophical). Furthermore, the study investigated whether Michigan's nonmedical vaccine exemption policy change had an impact on type-specific vaccine exemption clusters following its implementation.

Methods: The study used the ArcGIS optimized hot spot analysis tool to visually examine vaccine exemption clustering by type in Michigan. The study analyzed secondary kindergarten vaccine exemption data from 2301 elementary school buildings in Michigan for years spanning 2008 to 2015 and 2016 to 2017 post policy change.

Results: Clustering of vaccine exemptions by type was present both before and after implementation of the policy with fewer statistically significant features and differences regarding the distribution of hot spot clusters following the policy change.

Conclusion: Considering the heterogeneity in vaccine exemption hot spot clustering by type can help to inform public health officials to areas/communities at high risk for vaccine preventable disease outbreaks. Such analysis can allow for the implementation of vaccine exemption interventions that are exemption type specific and tailored for a given area, thus maximizing impact and making best use of limited public health resources. This analysis was also able to showcase the impact of Michigan's nonmedical vaccine exemption policy on vaccine exemption hot spot clusters.