Two measles cases reported in Chester County as officials reveal more data on Pa.’s outbreak
The state has seen 110 measles cases this year, nearly seven times the caseload in 2025.
Nineteen people have been hospitalized for measles since April in Pennsylvania, state health officials reported in a new online data dashboard launched this week to track the spread of the highly contagious disease.
Since April, an outbreak centered in Lancaster County has sickened 98 people — about a third of whom were under 18.
The virus is also circulating in western Chester County, on the border between the Philadelphia area’s suburbs and Lancaster in central Pennsylvania. The county reported two additional cases this week, bringing its total to six since the outbreak began.
The state has seen 110 cases this year, nearly seven times the caseload in 2025 and the largest case count in three decades. None of the patients sickened this year were fully vaccinated against the disease, state health officials said.
On the new dashboard, officials also highlighted ongoing vaccination efforts in affected counties, noting that this year state health workers have given out more than 600 doses of measles, mumps, and rubella vaccine in Lancaster County alone — more than three times the doses administered there in all of 2025.
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Secretary of Health Debra Bogen said in a statement that the measles dashboard launched as part of ongoing efforts to “boost public access to information and provide transparency in our work to protect public health.”
After The Inquirer and the Pittsburgh Post-Gazette earlier this year published analyses on school-level vaccination data that were not readily available to the public, the state committed to publishing that information on its website. The data will be available by August, officials said.
New cases near Philadelphia
Lancaster County has been a particular hot spot for measles, with 59 cases reported since April.
Last month, Chester County became the first in the Philadelphia region to identify measles cases since the current outbreak began.
As of Thursday, six people in the county had been diagnosed, county officials said. A seventh case was reported earlier this year during a separate outbreak.
All of the cases in Chester County were identified after patients sought medical care, but none have been hospitalized, said Nancy Sullivan, supervisor of the county’s disease investigation and surveillance program.
Most of the patients in Chester County contracted measles — which can infect up to 90% of unvaccinated people exposed to the disease — because they lived with another measles patient, Sullivan said.
“Individuals in the household are incredibly high risk; it’s not surprising to me that most [cases] are household contacts,” Sullivan said.
The county has not identified cases contracted through “community transmission,” when a person in a public place like a library or supermarket exposes others to the disease.
Still, physicians working in Lancaster have said they believe the true number of measles cases in Pennsylvania is higher than reported.
With cases circulating in the western part of Chester County, on the border with Lancaster County, Sullivan also suspects more cases are going unreported.
“We’re looking for community transmission and trying to stop that as quickly as possible,” she said.
County officials have encouraged residents to ensure they are up-to-date on measles vaccinations, directing locals to clinics hosted by the state health department.
If they are not able to attend those, Sullivan said, health workers will point them to Chester County’s own vaccination clinic, or even drive to residents’ homes to vaccinate them.
The county is also in daily communication with Philadelphia regional health officials, who have been closely monitoring infectious diseases amid a full slate of high-profile summer events in the area.
