Impact of Connecticut's 2021 Repeal of Religious Vaccine Exemptions on Kindergarten Vaccine Coverage

Importance: Religious vaccine exemptions remain central to debates over school-entry immunization mandates, but evidence on exemption repeal outside outbreak-driven policy responses and across communities with different religious contexts remains limited. Objective: To estimate changes in kindergarten vaccination coverage associated with Connecticut's 2021 repeal of religious vaccine exemptions, examine variation by school type and local religious congregation density, and compare trends with states that retained exemptions. Design/Setting/Participants: Interrupted time series analysis using kindergarten vaccination data from 2012-2025. Vaccine coverage trends in Connecticut were compared to Arizona, Louisiana, and Oregon, which retained religious exemptions during the study period. Intervention: The intervention studied was Public Act 21-6, which eliminated religious vaccine exemptions from school-entry immunization requirements. Main Outcomes and Measures: Outcomes included annual coverage for measles-mumps-rubella (MMR), varicella, diphtheria-tetanus-acellular pertussis (DTaP), polio, and hepatitis B vaccines. Models estimated pre-policy trends, immediate level changes, and post-policy slope changes. Analyses were stratified by public and private schools and by county-level religious congregation density. Results: Before policy implementation, kindergarten vaccination coverage in Connecticut declined across all vaccines by 0.16-0.20% per year (p < 0.001). Repeal of the religious exemptions occurred during a period of increasing religious congregation density and was associated with improved school-entry vaccination coverage, with annual coverage increasing 0.88-1.02% per year (p < 0.001). Coverage increased in both public and private schools, with larger post-policy gains in private schools. Coverage increases did not differ significantly between high- and low-religiosity counties. In segmented regression analyses, Connecticut's post-policy MMR slope was significantly higher than those of Arizona, Oregon, and Louisiana by 1.36, 1.71, and 1.15 percentage points per year, respectively (p < 0.001). By 2024/25, Connecticut MMR coverage reached 98.2%, exceeding coverage in comparison states by 5.6-9.6%. Cumulatively, the model-estimated policy impact represented an estimated 2,579 additional kindergarteners immunized against MMR compared with the no-policy counterfactual. Conclusions and Relevance: Connecticut's repeal of religious vaccine exemptions was associated with increases in kindergarten vaccination coverage across public and private schools, independent of local religious congregation density. These findings suggest that removal of religious vaccine exemptions may be an effective policy approach to improve childhood immunization coverage.