The Relationship Between State Vaccination Exemption Policies and MMR Vaccination Trends in the U.S.

MMR vaccination rates have been declining in the U.S. since the start of the COVID-19 pandemic, coinciding with an increase in the number of reported measles cases. However, vaccination trends are not uniform across states. Vaccination policies also differ across states, specifically their allowance of non-medical exemptions (NMEs). NMEs are classified as religious or personal/philosophical exemptions from vaccination requirements and allow parents to opt their children out of required (school-entry) vaccinations while still enrolling them in school. Previous studies have raised concerns about the impact of NMEs on declining MMR vaccination coverage, which has been identified as a contributing factor to measles outbreaks in the U.S. Despite these concerns, most states in the U.S. allow for at least one type of NME, with only five states prohibiting NMEs (as of June 20, 2025). Furthermore, in 2024 at least 15 states proposed new legislation to increase access to vaccination exemptions, indicating a worrisome trend in the U.S. vaccination policy landscape.

In this study, we present results from a two-phase analysis that further elucidates the relationship between state-level NME policies and MMR vaccination trends across the U.S. in the post pandemic era. First, for each of the 33 states represented in our previously published county-level data set (which is limited to 33 states due to data availability), we used a paired sign-test to identify the states with significant changes in county-level MMR vaccination rates between the pre and post pandemic periods. The outcomes of the statistical tests are illustrated alongside each state's NME policy in Fig. 1, and summarized in Table S1. Consistent with Dong et al., pre pandemic vaccination rates are defined as the average of the annual MMR rates for the 2017-18, 2018-19, and 2019-20 school years, and post pandemic rates are equivalently defined for the 2022-23 and 2023-24 school years to enable the most complete and robust representation across counties. The paired sign-test revealed that 26 of the 33 states experienced statistically significant changes in county-level MMR vaccination rates between the pre and post pandemic periods. Most critically, only four of the 33 states (New York, Maine, Connecticut, and California) experienced a statistically significant increase in MMR rates. Of these four states, New York, Maine, and Connecticut repealed NME options between the pre and post pandemic periods (2019, 2021 and 2021 respectively), while California's state policy prohibiting NMEs was in place across the full study period. In contrast, the states with the largest (and statistically significant) declines in MMR rates are those that allow both religious and philosophical exemptions - the policy with the most avenues for parents to opt out of vaccines for their children. Of the six states with insignificant changes in MMR rates, two (Rhode Island and Hawaii) are due to small sample sizes (5 and 4 counties, respectively), while the other four (Colorado, Nevada, Maryland and Vermont) reflect minimal changes in MMR rates. These findings qualitatively capture the relationship between state vaccination policies and MMR vaccination trends and motivate the second phase of our analysis.