The United States has now recorded more than 5,000 measles cases this year, the highest annual total since 1991, according to data from the Centers for Disease Control and Prevention (CDC) released on Friday.
The agency counted 5,182 confirmed cases in 2026, more than twice the 2,289 recorded in all of 2025. About 96% of this year's cases were in people who were unvaccinated or whose vaccination status was unknown.
Pennsylvania has been hit hardest, with 1,487 cases, followed by South Carolina and Utah. The CDC says 562 people, about one in nine of those infected, have been treated in hospital, and it has recorded four measles-related deaths this year. There have been 43 new outbreaks in 2026.
Measles is one of the most contagious diseases known, but it is preventable: two doses of the MMR vaccine are about 97% effective. Health experts say around 95% of a community needs to be vaccinated to stop outbreaks, and childhood vaccination rates in the US have fallen below that level in recent years.