Two Chester County residents have been diagnosed with measles, local health officials said on Tuesday, the first cases reported in the Philadelphia region this summer.
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Pennsylvania has identified 87 measles cases so far this year, the highest case count in three decades and more than five times the cases reported in 2025.
Chester is now the seventh Pennsylvania county with confirmed measles cases since April.
Jeanne Franklin, the county’s public health director, said it was too early to tell whether the two adults’ cases were linked to a growing measles outbreak centered in Lancaster County, which borders Chester.
Health workers in Chester County have conducted contact tracing regularly for months, speaking to about 100 people since the beginning of the year who had come into contact with someone with measles.
“The process is working,” Franklin said. She added that the county is preparing to identify more cases as they continue contact tracing.
The two Chester County residents with measles had initially sought care in Lancaster County, she said, and county officials were still working to determine their vaccination status.
Earlier in June, Delaware County health officials announced they had detected measles in wastewater samples, meaning a person with measles — either a resident or a person passing through the county — had used a bathroom connected to the county’s public water supply.
Since late April, officials have recorded 43 cases in Lancaster County, 20 in Lebanon County, six in Northumberland County, two each in Berks, Chester, and Dauphin Counties, and one in York County. (A winter outbreak saw 12 cases among Chester, Montgomery, and Lancaster Counties.)
The current outbreak is spreading largely among people who are unvaccinated, state officials have said.
The public health threat remains unpredictable in the Philadelphia metro area, where a recent Inquirer analysis found under-vaccinated pockets pose a rising risk to a region with higher overall vaccination rates.
Franklin said her department is increasing public communications about the measles risk, and encouraging local health providers to vaccinate infants with a “dose zero” of the measles, mumps, and rubella shot.
Typically, children receive an MMR dose at around one year old and before entering kindergarten. A “dose zero” is given at six months and provides additional protection before children receive two more doses of the vaccine.
State officials last week also recommended that physicians in affected areas provide early measles vaccinations to infants and young children.
Chester County officials are also working with the state to analyze school-level vaccination data to pinpoint at-risk communities, Franklin said.
Overall, 94.5% of Chester County kindergarteners were vaccinated against measles in the 2024-2025 school year, the last for which data is available. That’s just below the 95% threshold required to prevent the spread of the virus.
Spread may be wider than cases reported
Some providers in Lancaster County have said that they fear measles is spreading more widely than state officials have been able to track, either because patients don’t realize the importance of informing health officials about their condition or are avoiding providers.
Chester County also is contending with uncertainty. Franklin said that some residents who have had contact with infected patients have told health workers that they’d rather not get tested for measles.
“They say, ‘I don’t want to be tested. Let this run the course,’” she said.
Contact tracers stress that they’re not judging that decision, she said. But the department emphasizes that they need residents to work with contact tracers, so other potentially exposed families can make informed decisions about their health.
Franklin urged Chester County residents to check their vaccination records to ensure they are protected against measles, which can infect up to 90% of unvaccinated people exposed to the disease.
If they can’t find their records, a primary care physician can order a test to determine whether they’re immune.
Residents should also look out for symptoms of measles, including a fever, a cough, and a runny nose — similar to other respiratory diseases — that often emerge before patients develop a telltale rash.
Several people sickened this summer have experienced severe illness and required hospitalization for serious electrolyte abnormalities and liver and kidney dysfunction, according to physicians in Lancaster County.
“If you previously decided not to get a vaccine, this is the time to reconsider, based on what’s going on,” Franklin said. “The window to get a vaccine once you’ve been exposed is very small.”
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