A recent study indicates that rates of measles, mumps, and rubella (MMR) vaccinations among children in the United States have decreased since the COVID-19 pandemic began.
The study, published in JAMA on June 2, assessed MMR vaccination rates at the county level, using available data. Researchers from Johns Hopkins University gathered data on MMR vaccination rates for kindergarten students from each state’s health department website for the school years before (2017-2018) and after (2023-2024) the pandemic. When this data was unavailable, they used the most comparable data.
Out of 2,066 counties across 33 states, 78% showed a decline in vaccination rates. The study revealed that the average county vaccination rate fell from nearly 94% pre-pandemic to around 91% post-pandemic, which is below the 95% threshold needed for herd immunity against measles.
, the study’s senior author and director of Johns Hopkins University’s Center for Systems Science and Engineering, stated that the research aimed to gain a “more comprehensive, higher resolution understanding of the vaccination landscape” in the U.S.
According to the CDC, vaccination patterns can vary significantly within a state and even within communities inside a county. Gardner explains that low vaccination rates in some areas increase the likelihood of measles outbreaks. “And that’s what we’re seeing.”
As of May 29, 2025, 1,088 measles cases had been confirmed across 33 U.S. jurisdictions. Of these, 96% occurred in individuals who were either unvaccinated or had unknown vaccination status. In 2025, there have been 14 reported outbreaks and three confirmed measles-related deaths, all among . Before 2025, the last confirmed measles-related death in the U.S. occurred in 2015.
Vaccination is the most effective way to prevent measles. The MMR vaccine is considered safe and effective, with the CDC stating that most vaccinated individuals are protected against measles for life.
The study indicated that only four of the 33 states analyzed—California, Connecticut, Maine, and New York—saw an increase in median county-level vaccination rates. Researchers did not examine the reasons for these rate differences, but Gardner suggests that various factors, like the pandemic’s effect on healthcare access, population differences, data quality, and vaccine hesitancy, may contribute. She also pointed out that the four states with increased rates have mandates for school immunizations, including the MMR vaccine.
Gardner highlighted Hawaii’s significant drop in measles vaccine coverage, from around 95% before the pandemic to approximately 80% after. Wisconsin had the lowest average vaccination rate among the studied states, with its most recent rate in the 70s.
Gardner noted that a state’s average vaccination rate can be misleading due to community-level variations. She suggested that analyzing vaccination rates at the school level would provide even more valuable data.
“The higher granularity you get, the more you actually see problems—and then can also respond to them and figure out where it’s actually important to go and target and try and help get vaccination rates up,” Gardner stated.
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