• Posted June 3, 2025

Measles Vaccinations Declining Throughout U.S.

Declining vaccination rates are making more and more U.S. children vulnerable to measles and mumps, a new study says.

A national decrease in MMR (measles/mumps/rubella) vaccinations among American children has occurred since the start of the COVID-19 pandemic, researchers reported June 2 in the Journal of the American Medical Association.

More than three-quarters of U.S. counties (78%) have reported drops in vaccinations, researchers found.

Only four of 33 states studied – California, Connecticut, Maine and New York – have reported increases in MMR vaccinations, results show.

These results come as measles outbreaks sweep through parts of the U.S., with more than 1,000 cases reported this year in 31 jurisdictions, researchers said in background notes.

“If vaccination rates continue to decline, measles is likely to return to endemic levels in the U.S.,” wrote the research team led by senior researcher Lauren Gardner, a professor at Johns Hopkins Whiting School of Engineering who is an expert in using data and modeling to understand the spread of disease.

For the new study, researchers developed a new county-level MMR vaccination database to complement state- and national-level data collected by the U.S. Centers for Disease Control and Prevention (CDC).

“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,” Gardner said in a news release.

Gardner previously led collection efforts behind Johns Hopkins' COVID-19 dashboard, which provided a global means of tracking the pandemic.

For this study, her team looked at MMR vaccination rates for kindergarteners from 2017 to 2024. The county-level data on those who received two doses of the vaccine were collected from state websites.

The analysis shows that average county-level vaccination rates fell from 93.9% pre-pandemic to 91.2% post-pandemic, an average decline of about 2.7 percentage points.

This shows the nation moving farther away from the 95% vaccination rate required for herd immunity against measles, which is an incredibly virulent infectious disease, researchers concluded.

The CDC estimates that if a person has measles, up to 90% of the people close to them will also become infected if they aren’t vaccinated. Measles can live for up to two hours in a room’s air after an infected person has left.

More information

The U.S. Centers for Disease Control and Prevention has more on how measles spreads.

SOURCE: Johns Hopkins University, news release, June 2, 2025