Montgomery County's confirmed measles cases jumped from zero to three in the span of a week, according to Metro Philadelphia's reporting on state data released Sept. 11.
The uptick arrives as Pennsylvania recorded its third measles death of 2026. A 40-year-old unvaccinated woman in Jefferson County died Saturday, Sept. 12, from measles complications, Jefferson County Coroner Greg Furlong confirmed. The state's case count has reached 676 across 37 counties. Of those, 124 people have been hospitalized, according to Patch.
Pennsylvania has surpassed South Carolina as the hardest-hit state in the largest U.S. measles outbreak since 1991, with 3,294 cases nationally as of Sept. 10.
Colonial schools below the threshold
For families in the Colonial School District, the outbreak carries a specific warning. Montgomery County's kindergarten MMR vaccination rate slipped to 94.8% in the 2025-26 school year, falling below the 95% herd-immunity threshold for the first time, according to a Philadelphia Inquirer analysis of state data. The county had been the only one in the Philadelphia region at herd immunity two years earlier.
The gap is wider at the youngest grades within Colonial schools. Plymouth Elementary School's kindergarten MMR rate was 93.7% among 159 students, according to state data reported by Patch. Colonial Middle School's seventh-grade rate was 98.3% among 422 students. Plymouth-Whitemarsh High School seniors were at 99.0%.
Statewide, 93% of kindergarteners were fully vaccinated, compared to 97% of 12th-graders, according to Pennsylvania Secretary of Health Dr. Debra Bogen.
A growing toll
The two earlier Pennsylvania deaths, both in August, involved Lancaster County infants too young to be vaccinated, CBS News reported. Lancaster County remains the outbreak's epicenter with 295 confirmed cases.
The Jefferson County woman's death certificate lists respiratory failure caused by suspected measles, along with chronic obstructive pulmonary disease and asthma, according to Medical Daily. She declined testing before she died, so the state has not formally classified her death as measles-associated. The Pennsylvania Department of Health said it is reviewing the case.
"This is a heartbreaking loss for the family and an unfortunate reminder that measles can be a serious and potentially life-threatening disease," Furlong said.
CDC Director Dr. Erica Schwartz said in a statement that the agency was not notified of the death by Pennsylvania officials and that the state has not requested federal on-the-ground outbreak support, 6abc reported.
Vaccination demand surging
Providers across Pennsylvania administered more than 46,000 MMR doses in August, nearly double the typical monthly pace of 25,000, according to WGAL's reporting on Bogen's update. State health staff have hosted more than 120 pop-up vaccination clinics since the outbreak began in late April, providing nearly 4,300 doses.
Fewer than 1% of the state's 676 confirmed cases occurred in vaccinated people. None of the four vaccinated patients who tested positive required hospitalization, according to Bogen.
Gov. Josh Shapiro said at an Aug. 26 press conference that a tripling in the rate of families seeking philosophical or religious exemptions over the past decade has contributed to declining vaccination rates.
Montgomery County residents who suspect measles exposure can call the county Office of Public Health at 610-278-5117 before leaving home. The state's toll-free measles hotline is 877-PA-HEALTH (877-724-3258).
