As of Thursday, nearly 4,600 measles cases had been confirmed in the United States this year, according to the CDC. That's more than double the number for all of 2025.
96 percent of those infected were either unvaccinated or had an unknown vaccination status.
Pennsylvania has been hardest hit, with the Department of Health reporting more than 1,300 cases in 2026 on Friday. Five people have died in the state, three of them in communities dominated by the Amish religious movement, according to NPR.
The CDC urges vaccination. The most vulnerable are children who are still too young to be vaccinated.
"Babies are easy victims. It's incumbent on all of us to protect all of us," pediatrician Deborah Greenhouse told the AP earlier this year.