Hundreds of Philadelphia-area Schools Fall Below Measles Herd Immunity Threshold

State health officials released school-level immunization data showing that 40% of kindergarten classrooms in the five-county Philadelphia region were vulnerable to a measles outbreak during the 2025-26 school year, up from 33% the previous year. At least 249 schools reported measles vaccination rates below the 95% herd-immunity benchmark, and 98 of those schools had rates under 90%, according to the analysis.

The decline is most pronounced in schools where parents have opted out of vaccines for religious or philosophical reasons; exemptions in those categories rose 15% over the past two years. Pennsylvania is one of the few states that permits such exemptions with a signed form.

Governor Josh Shapiro, speaking at a news conference about the state’s first measles-related deaths in three decades, said the trend has "dramatically reduced community immunity" and emphasized the importance of the newly published data for families to make informed decisions.

Philadelphia school district medical director Kendra McDow attributed the drops to growing vaccine hesitancy and noted that families are often confused by mixed messages at the national level. "What we’re seeing is reflective of what I believe are local and national trends," she said.

The outbreak, which has produced nearly 400 confirmed cases—about half in Lancaster County—has also claimed two lives. Chester County, bordering Philadelphia, reports the second-highest case count in the state.

Public health officials warned that even modest declines can increase risk because measles can remain airborne for hours and infect up to nine out of ten unvaccinated individuals. Rene Najera, director of public health at the College of Physicians of Philadelphia, said lower vaccination rates endanger not only schoolchildren but also pregnant women, cancer patients and infants too young for immunization.

Local health departments are urging schools to identify unvaccinated students and staff and to develop contingency plans, including a 21-day exclusion period for anyone exposed to a confirmed case. "You don’t own getting them vaccinated, but you have to think through these things," Chester County health director Jeanne Franklin said.

The Philadelphia School District continues to operate summer and year-round vaccination clinics, offering extended hours and weekend sessions to improve access. At a recent back-to-school fair, families lined up for immunizations, with some citing transportation or language barriers as obstacles to vaccination.

Officials hope that increased transparency and outreach will help reverse the downward trend and protect the community as the measles outbreak spreads toward the densely populated city.