US measles cases reach 35-year high with Pennsylvania’s outbreak driven by vaccine hesitancy

The United States reports its highest measles case count in over three decades, with Pennsylvania experiencing its largest outbreak yet, as vaccine misinformation hampers immunisation efforts and causes deadly consequences.

Pennsylvania has confirmed a fifth measles-associated death as the United States records the highest number of measles cases in more than three decades, underscoring how quickly the disease is spreading in communities with low vaccination coverage. State health officials said the latest death involved an unvaccinated Lancaster County resident who had tested positive for measles. The Pennsylvania count now stands at 943 cases across 39 counties this year, with the state’s outbreak becoming the largest active one in the country.

The Associated Press reported that the latest death adds to a grim toll in Pennsylvania, where the other fatalities linked to measles this year included a teenager, a 40-year-old woman and two infants who were too young to receive the vaccine. Public health officials say the state has not seen measles deaths in 35 years, highlighting how unusual and serious the current surge has become.

According to the Pennsylvania Department of Health, more than 53,000 MMR vaccine doses were administered across the state in September, more than double the usual monthly total. Health officials say the vaccine remains highly effective, with two doses providing 97% protection against measles. The state’s case total is approaching South Carolina’s outbreak last year, which reached 997 confirmed infections before ending in April.

Nationally, the Centres for Disease Control and Prevention said the country had recorded 3,659 confirmed cases as of September 24, spread across 45 states and the District of Columbia. That total is well above the 2,289 cases reported in all of 2025 and marks the highest yearly count in 35 years. The CDC says measles is extremely contagious and that around 95% of this year’s cases involved people who were unvaccinated or whose vaccination status was unknown, a pattern that public health experts say reflects falling immunisation rates and persistent vaccine misinformation.