A fourth person has died of measles in Pennsylvania, as the state's outbreak—the worst in more than three decades—approaches 700 cases. The latest victim, an unvaccinated 18-year-old from Mifflin County, died from acute disseminated encephalomyelitis (ADEM), a rare but recognised severe complication in which inflammation strips the protective coverings from nerve cells in the brain and spinal cord. The state also confirmed the death of an unvaccinated 40-year-old woman from Jefferson County, adding to two earlier infant deaths in Lancaster County. The deaths underscore the risks of the ongoing outbreak, which state health officials say is being fuelled by low vaccination rates.

Pennsylvania has now recorded 693 measles cases across 38 counties this year, with 99 in the past week alone and 133 people hospitalised. Health Secretary Debra Bogen urged residents to get the MMR vaccine, which has historically kept outbreaks under control. The deaths are unlikely to be swiftly reflected in national figures, as the CDC—now overseen by vaccine-sceptic Health Secretary Robert F. Kennedy Jr—has altered its reporting methods and reportedly excluded some deaths, even as it says nearly 3,300 cases have occurred nationally this year, surpassing last year's record of 2,289 cases and three deaths.