Pennsylvania has the most cases of any state, with 1,136, followed by South Carolina with 671 and Utah with 527. Nearly every state has reported at least one case this year, and the outbreak has been spreading in the U.S. for close to two years.

Health and Human Services Secretary Robert F. Kennedy Jr. has attributed the surge to unvaccinated populations left over from the COVID-19 pandemic, pointing to a 2020 diary entry by Anthony Fauci predicting that more than 1 million children worldwide would miss vaccinations because of pandemic shutdowns. Kennedy said the U.S. is doing better than other countries on measles. He cited six probable measles deaths in the U.S. so far this year.

Kennedy has called the MMR vaccine "the most effective way of stopping measles spread." He has also said at a Children's Health Defense conference that conditions including autism and asthma are common side effects of the vaccine.

MMR vaccination rates among kindergarteners fell to 92.4 percent for the 2025-2026 school year, below the 95 percent threshold public health officials say is needed to prevent outbreaks. A CDC vaccine advisory panel that Kennedy restaffed voted to reduce the recommended childhood vaccine schedule; a federal judge blocked those votes earlier this month.

The U.S. declared measles eliminated in 2000. It risks losing that status after a Pan American Health Organization meeting scheduled for November. Amria Roess, a professor of global health and epidemiology at George Mason University and a former CDC officer, said in a university-published tip sheet that the likely loss of elimination status is an indicator of "our eroding public health system."