In a recent study published in Vaccine, researchers from Johns Hopkins University’s Center for Systems Science and Engineering and Department of Civil and Systems Engineering find that state policies allowing non-medical vaccine exemptions, shortened to NMEs, are statistically linked to lower measles-mumps-rubella, or MMR, vaccination rates in the post-COVID-19 era, a period in which the majority of U.S. counties fall below the 95% immunity threshold needed to predict or limit the spread of measles.
The researchers’ findings show the largest declines in coverage occurred in states that permit both religious and philosophical vaccine exemptions, which allow parents to opt out of state-mandated vaccination for their children for personal reasons.
“We conducted this study to determine if there was evidence of the relationship we hypothesized to exist between state non-medical exemption policies or policy changes and the trends we were observing in MMR coverage across the country,” says Samee Saiyed, lead author and civil and systems engineering PhD student.
The team’s work builds on prior research led by Lauren Gardner, principal investigator, CSSE director, and Alton and Sandra Cleveland Professor of Civil and Systems Engineering, which documented a nationwide decline in childhood MMR coverage following the pandemic.
“The results of the study are extremely relevant, given recently passed and pending state legislation to increase vaccination exemptions in more than 15 states and Florida’s announcement of plans to repeal all vaccine mandates statewide,” says Gardner.
Gardner’s team analyzed available county-level data for 33 states and found that 26 states experienced statistically significant changes in MMR vaccination rates between pre- and post-pandemic periods. Only four states—New York, Maine, Connecticut, and California—saw increases, and all met or exceeded the 95% immunity threshold. Three of the four states that experienced increases had repealed NME options during the study period, which included the 2017-2018 school year through the 2023-2024 school year, while California’s prohibition on NMEs was in place throughout.
On average, states allowing both religious and philosophical exemptions saw declines of 3.77%, while states allowing only religious exemptions declined by 2.3%. States prohibiting NMEs reported a modest average decrease of 0.78% but remained well above 95% both before and after the pandemic. States that repealed NMEs during the study period recorded an average MMR vaccination increase of 1.66%.
“Our findings reinforce concerns about the relationship between vaccine exemption policies and declining vaccination coverage in the post-pandemic era, and suggest that increasing NME options could lead to further reductions in MMR vaccination and an increased risk of measles outbreaks,” Saiyed says.
As part of their ongoing research, the team is using individual-level survey data to better understand the factors driving vaccine-related beliefs, attitudes and decision making, and how they relate to population-level outcomes.
The timeliness of their research is underscored by Canada’s recent loss of measles elimination status, reinforcing the importance of vaccination to prevent consequences of infection, including the potential loss of elimination status in the U.S.
“Understanding the relationship between NMEs and MMR vaccination rates is a critical step in guiding evidence-based vaccine policy and intervention as vaccination remains the foremost tool to prevent measles infections and deaths,” says Saiyed.