School-entry vaccine exemptions in Maine before and after public law 154, 2018–2023

Maine passed Public Law (PL) 154 in 2020, eliminating new non-medical exemptions (NMEs) to school-entry immunization requirements. We examined how this policy change affected vaccine exemption rates and clustering in kindergartens using annual, publicly available school-level counts of vaccine exemptions from the Maine Center for Disease Control and Prevention. Although NMEs decreased significantly, medical exemptions (MEs) increased and began clustering in kindergartens after PL 154's implementation in 2021. This perpetuated the increased likelihood that children with exemptions, primarily MEs post-PL 154, interact with one another in school. The emergence of clusters of kindergartens with statistically significantly higher ME rates relative to the population average may create or reinforce existing under-immunized pockets at higher risk of vaccine-preventable diseases. Our results demonstrate that eliminating NMEs can substantially reduce overall school-entry vaccine exemption rates, while underscoring the need for additional guidance to support states in implementing these policy changes.