Infantile vaccination rates against measles, mumps and rubella has decreased in a large part of the United States since the start of the Pandemic COVID-19, a new study revealed.
The study, which was published in Jama On June 2, analyzed the vaccination rates of measles, mumps and rubella (MMR) by county where data was available. Researchers at Johns Hopkins University have collected data on the county on MMR vaccination rates for children’s gardens on the health service of each state for school years before the pandemic (2017-2018) and after (2023-2024). In states where these data were not available, researchers rather analyzed the most comparable data.
Of the 2,066 counties in 33 states that researchers have analyzed, 78% of them reported a drop in vaccination rates. The researchers found that the average vaccination rate at the county level had increased from almost 94% before the pandemic at around 91% after the pandemic, moving well below what public health experts generally consider as the threshold for the immunity of the herd against measles of around 95%.
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Lauren Gardner, the main author of the study and director of the Center for Systems Science and Engineering of Johns Hopkins University, said that the objective of this research was to obtain a “more complete understanding and more resolution of the country’s vaccination landscape.
The American centers for the control and prevention of diseases (CDC) “have data at national and national level, but we know that vaccination models can vary considerably within a state and even to a higher resolution than that between communities, in even the county,” explains Gardner. For places with a low vaccination rate, “if measles is introduced in these regions, there is more faith. And that’s what we see. “
As of May 29, a total of 1,088 confirmed measles cases were reported by 33 jurisdictions in the United States, according to the CDC. Among these cases, 96% were in people who were not vaccinated or whose vaccination status was unknown. Until now, in 2025, 14 epidemics have been reported and three people have been confirmed as died of complications related to measles, which have not been vaccinated. Before this year, the last confirmed death linked to measles in the country took place in 2015.
Being vaccinated is the best way to be protected from measles. The ROR vaccine is both safe and effective, and the CDC said that most people who get it will be protected from measles for life.
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The new study revealed that only four of the 33 states that researchers have analyzed – California, Connecticut, Maine and New York – said an increase in median vaccination rates at the county level. The researchers have not studied the causes behind the disparate rates, and Gardner says that many factors – including the impact of the pandemic on access to health care, the different populations, the quality of the reported data and the hesitation of vaccines – play a role in the vaccination rates of a community. But it also notes that the four states that have reported an increase in the rate of measles vaccination are among the rare which do not allow non -medical exemptions for the requirements of school immunization, such as the ROR vaccine.
Gardner says that Hawaii stood out towards her in the study because she experienced a significant decrease in the coverage of measles vaccines; Before the pandemic, its rate was around 95%, but after the pandemic, it dropped to around 80%. Wisconsin had the lowest vaccination rate, on average, among the states studied; Its most recent rate was in the 1970s.
Gardner says that the average vaccination rate of a state could be misleading because the rate can vary considerably within the communities. It would be ideal, she says, if researchers could become even more granular with data and analyze vaccination rates at school by school.
“The higher you get higher granularity, the more problems you see – and can also answer it and determine where it is really important to target and try to help get vaccination rates,” explains Gardner.
