Pennsylvania is experiencing the largest measles outbreak in the country, with over 700 confirmed cases and four deaths since April. The outbreak, centered in Lancaster County, has hospitalized 150 people and spread to 38 of the state's 67 counties. More than 3,400 measles cases have been reported across 45 states this year.

The surge has prompted a significant increase in vaccinations, with an 84 percent increase in August, according to state health officials. However, defiance and resignation persist, particularly among Amish and Mennonite communities. In Lancaster County, about 60 miles west of Philadelphia, some residents remain unvaccinated despite the risks.

Declining vaccination rates nationwide since the Covid-19 pandemic have fueled the outbreak. U.S. kindergartner vaccination coverage dropped to about 92.4 percent in the 2025-2026 school year, below the 95 percent needed for herd immunity. Pennsylvania has the largest number of Amish in the country, according to the Young Center at Elizabethtown College.