Measles vaccination rates in children have declined in most U.S. counties, study finds

Amid a widespread decline in childhood measles vaccination rates since before the COVID-19 pandemic across the United States, a study published Monday found that coverage can vary substantially within a state.

Looking at county-level data in 33 states, researchers at Johns Hopkins University found that the MMR (measles, mumps and rubella) vaccination rate decreased from 93.92% in the 2017-2018 school year to 91.26% in the 2023-2024 school year. Other states were not included because they had missing vaccination data, the authors of the study said. 

Of the 2,066 counties the study looked at, 78% saw a decline in vaccination rates. Only four of the 33 states — California, Connecticut, Maine and New York — saw an increase in the average county-level vaccination rate, the study found.

The data shows significant diversity in the levels of vaccination within and across states, which the authors of the study say could “help inform targeted vaccination strategies.” 

The study comes amid the largest measles outbreak in the U.S. since a 2019 wave. Across the country, 1,088 cases of the disease have been reported, according to data from the Centers for Disease Control and Prevention as of May 30. Most of those cases are in West Texas. 

Texas is an example of a state where vaccination rates vary across counties. 

“If you focus in on Gaines County in West Texas with a vaccination rate of just over 80%, that is the epicenter for the measles outbreak in West Texas, showing how vulnerable some of these areas can be,” Dr. Céline Gounder, a CBS News medical contributor and editor-at-large for public health at KFF Health News, said Monday on “CBS Evening News.”

Among the reported U.S. cases, 96% are either unvaccinated or have an unknown vaccination status, according to the CDC. Measles, a highly contagious disease, can lead to serious health complications or death. The MMR vaccine is highly effective and safe, the government agency says.

The CDC has also reported state-level declines in vaccination coverage for kindergartners by school year, saying the rate among U.S. kindergartners has decreased from 95.2% during the 2019-2020 school year to 92.7% in the 2023-2024 school year. 

When more than 95% of a community is vaccinated, it reaches herd immunity, making it very difficult for the disease to spread, according to the CDC.

“There’s a lot of counties that are well below the 95%, so we’re quite vulnerable, in certain pockets in particular of the country, for a measles outbreak,” Gounder said.