New data shows MMR vaccination rate decline across the U.S.

A new county-level dataset from Johns Hopkins University researchers reveals a national decline in the measles-mumps-rubella, or MMR, vaccination rate among U.S. children since the start of the COVID-19 pandemic.

Image credit: Johns Hopkins University

Out of 2,066 counties studies, 1,614 counties, or 78%, reported drops in vaccinations. The average county-level vaccination rate fell from 93.92% pre-pandemic to 91.26% post-pandemic—an average decline of 2.67%, moving further away from the 95% herd immunity threshold to predict or limit the spread of measles.

Only four of the 33 states studied—California, Connecticut, Maine, and New York—reported an increase in the median county-level vaccination rate.

The data was published June 2 in JAMA .

The data is released as more than one thousand measles cases have been reported this year in the United States. With the exception of 2019, this is the most cases reported in the U.S. in a single year in over three decades, with the vast majority of cases occurring in unvaccinated children.

Image credit: Johns Hopkins University

"This open, high resolution dataset provides a critical resource to explore and better understand the country's vaccination landscape and its implications for the risk of measles spread," said senior author Lauren Gardner, director of Johns Hopkins University's Center for Systems Science and Engineering, an expert in using data and modeling to better understand the spread of disease. This work draws on her experience leading the data collection efforts behind the Johns Hopkins' COVID-19 dashboard that was relied upon globally during the pandemic.

The county-level vaccination data complements the state and national-level from the Centers for Disease Control and Prevention, confirming a widespread decline in MMR vaccination rates in the U.S. following the COVID-19 pandemic, while also revealing the significant heterogeneity of vaccination patterns within and across states.

The team collected county-level two-dose MMR vaccination rates for kindergarteners from each state's department of health website from 2017 to 2024, where available. The dataset includes at least one year of vaccination data for 2,237 counties across 38 states.

All data is available for download.

Authors include former adjunct assistant research scientist Ensheng Dong; graduate student Samee Saiyed; former research assistant Andreas Nearchou; and undergraduate student Yamato Okura, all of Johns Hopkins.