Pennsylvania health officials reported 767 confirmed measles cases statewide as of September 18, marking the largest outbreak in the country this year. The cases span 38 of the state's 67 counties, with Lancaster County accounting for the highest concentration at 324 infections.

The outbreak began in late April in the Lebanon and Lancaster counties region and has since accelerated, particularly during August and September. State data show 150 people have required hospitalization, and four measles-associated deaths have occurred among unvaccinated individuals, including two infants too young for vaccination, a 40-year-old woman, and an 18-year-old.

More than 99 percent of cases involve unvaccinated or under-vaccinated people. Only four confirmed infections occurred in individuals who received the recommended MMR doses for their age.

Pennsylvania Department of Health officials have responded with nearly 4,800 MMR vaccinations administered at 148 pop-up clinics since the outbreak started. An 84 percent increase in vaccinations occurred in August compared to prior periods. Additional clinics are planned in the coming weeks.

Nationally, more than 3,400 measles cases have been reported across 45 states in 2026, exceeding totals from recent years. Pennsylvania leads the country in confirmed infections.

The highly contagious virus has prompted increased public health efforts focused on contact tracing and community outreach. Officials continue to update a public dashboard with case counts, hospitalizations, and vaccination information.