Colonial School District's 5,700 students returned to classrooms across Conshohocken, Plymouth and Whitemarsh townships on Aug. 31, the same week Pennsylvania reported 80 new measles cases statewide.

Montgomery County's kindergarten MMR vaccination rate slipped to 94.8% in the 2025-26 school year, dropping below the 95% threshold public health experts consider necessary for herd immunity for the first time in more than two years, The Philadelphia Inquirer reported. About 40% of kindergarten classrooms across the Philadelphia region fell below that threshold, up from 33% the year before.

The state Department of Health announced Sept. 4 that confirmed measles cases had reached 577 across 37 counties, up from 460 reported around Aug. 30, according to WFMZ. The outbreak, the nation's largest, has hospitalized 98 people and resulted in two measles-associated deaths since it began in late April.

Schools across Bucks and Montgomery counties have begun issuing measles response protocols, The Reporter Online reported. Pennsbury School District in Bucks County is the only district named with specific plans so far. Superintendent Thomas A. Smith told parents his district had met with the Bucks County Health Department to establish response procedures, including removing an infected student from school, conducting contact tracing with public health officials and notifying families of possible exposure.

Neither Colonial nor Wissahickon School District has made public a specific measles protocol.

The Bucks County Health Department recommends families confirm their children's vaccinations are current and keep immunization records accessible. Two doses of the MMR vaccine are 97% effective against measles. One dose is 93% effective.

"This is obviously a deeply serious measles outbreak that we are dealing with all across the commonwealth of Pennsylvania … the situation has gotten much worse," Gov. Josh Shapiro said in Upper Moreland Township on Aug. 29, as reported by Glenside Local.

In August, more than 46,000 MMR vaccines were administered statewide, nearly double the roughly 25,000 doses given in a typical month, according to PennLive. State health officials have also run more than 100 pop-up vaccination clinics in affected communities since the outbreak began.

Lancaster County remains the epicenter, with more than 240 cases. About 30% of those infected statewide are under 18.

Parents can check school-level vaccination rates through a state tool launched Aug. 4. The Department of Health's measles dashboard tracks cases, hospitalizations and vaccination efforts, with updates on Mondays, Wednesdays and Fridays.