Pennsylvania health officials confirmed 89 new measles cases in the state in the last seven days, an escalation of a rapidly growing measles outbreak now impacting more than two dozen counties.
As of Thursday, Pennsylvania had reported the third-highest number of measles cases in the country for 2026, behind Utah and South Carolina, according to data from the Centers for Disease Control and Prevention.
Delaware has reported 22 cases this year, the first time in a decade that the highly contagious disease has been diagnosed in state residents. New Jersey has confirmed just one case.
In Pennsylvania, children made up about one-third of the 379 patients diagnosed with measles in two separate outbreaks so far this year, state officials say. None of the patients diagnosed with measles this year has been fully vaccinated.
In all of 2025, the state reported just 16 measles cases.
Lancaster County, with some of the lowest measles vaccination rates in the state, has been at the center of both Pennsylvania outbreaks this year. As of Friday, the county has tallied 181 cases.
State officials warned earlier this week that the public may have been exposed to the disease on Aug. 4 and 5 at a soccer camp at Millersville University and on Aug. 12 at a Whole Foods in Lancaster.
Chester County has the second-highest number of cases in the state, at 41; it is the only Philadelphia-area county to report cases in the current outbreak, which began in April.
And cases are climbing in central Pennsylvania, with Centre County reporting 13 cases and neighboring Mifflin County reporting 25.
State health officials said that 70 people, including 22 children, have been hospitalized with measles this year. That’s about 18% of the total cases reported.
In August alone, state officials have confirmed nearly 200 new cases in Pennsylvania.
The true number of cases is likely much higher, physicians and health officials in Lancaster and Chester Counties say.
In Chester County, some residents have refused to cooperate with health workers looking to trace their contacts to understand how measles is spreading in the county, officials there have said.
Local officials also worry about the spreading outbreak as many children return to school next week. Overall, about 93% of kindergarteners in Pennsylvania were vaccinated against measles, mumps, and rubella (MMR) in the 2025-26 school year.
That’s just below the 95% “herd immunity” threshold, the level at which scientists say a given population must be immunized to prevent the spread of measles, which can infect nine in 10 unvaccinated people exposed to it.
Analyses earlier this year by The Inquirer and the Pittsburgh Post-Gazette show pockets of vulnerability across the state, with hundreds of kindergarten classes reporting vaccination rates below herd immunity, putting students and communities at risk for an outbreak.
Still, most Pennsylvania students are fully vaccinated and schools “benefit from robust community immunity that serves as a powerful barrier against the virus,” state health officials said in a statement.
The state hosted medical briefings for nearly 1,000 school nurses over the summer to provide guidance on preventing measles as they prepare for the upcoming school year, officials said.
Most measles cases resolve in weeks with mild-to-moderate flulike symptoms, but the disease is particularly risky for young children and can result in severe complications, including death.
This year, Pennsylvania hospitals have treated adults with brain swelling and pneumonia, and children with dehydration or damaged organs from measles.
State officials have stepped up vaccination campaigns in response to the outbreak, with health department staff dispensing more than 4,000 vaccinations in the state this year — and more than 1,800 in August alone.
The department has held 85 pop-up clinics in affected counties since April and has scheduled “dozens” of additional clinics for the coming weeks and months.
The state has also hosted briefings for healthcare providers on how to recognize and treat measles, and is recommending that doctors offer early vaccinations for children as young as six months old in affected areas.
Read more on Pennsylvania’s measles outbreak
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Inside Pa.’s measles outbreak: A family rides out the virus, doctors treat severely ill children
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In Lancaster, measles cases are rising as providers try to combat low vaccination rates
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More than 200 Philly-area schools are vulnerable to a measles outbreak
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What are the measles vaccination rates in your district? See how your school compares.