Pennsylvania has not seen a measles year like this since 1991. As of September 11, the has confirmed 676 measles cases in 2026, spread across 37 of the state’s 67 counties. Two infants died in August, and on September 13, a county coroner reported the death of a 40-year-old woman. And Pennsylvania now reports more measles cases this year than any other state in the country, according to a .
This would have been hard to imagine a few years ago. , meaning the virus was no longer spreading continuously within the country. For two decades, the only cases we saw were sparks: a traveler brought the virus home, a handful of people got sick, and high vaccination rates kept the sparks from catching. Since last year, in Pennsylvania, Texas, Utah, and South Carolina, among other states, the sparks caught.
How the Outbreak Unfolded
The first few months of 2026 looked ordinary as far as measles outbreaks go. Twelve cases were identified between January and March, mostly in Lancaster County, with a few in Montgomery and Chester counties, and none of them connected to what came next.
The outbreak itself began in late April. to the Lancaster and Lebanon county area, where it spread through communities with low vaccination rates. By May 22, Pennsylvania had recorded 32 cases, already . By late June, there were 84. By late July, 114.
Then the curve bent sharply upward. The shows roughly 330 cases reported in August alone, more than in the first seven months combined, and September is on a similar pace. In the week before September 11, the state added 108 new cases. Lancaster County accounts for 295 cases, nearly half of the total, but the virus has traveled well beyond it: Mifflin County has 74 cases, Chester County has 65, and nine counties stretching from the Philadelphia suburbs to the western part of the state now have what health officials call community transmission, meaning the virus is passing from person to person over several generations without a clear outside source.
Three Deaths, the First in 35 Years
On August 25, the Pennsylvania Department of Health in Lancaster County. They were the first measles deaths in Pennsylvania in 35 years and, as , the first measles deaths reported anywhere in the United States this year. (In 2025, three deaths were reported in Texas [] and New Mexico [].)
We now know more about who the recent Pennsylvania fatalities were. According to details , both were infants. One was a newborn boy who died on August 14 of a ruptured spleen; he had been infected with measles before birth, and the infection is listed on his death certificate as a contributing condition. The other was a six-week-old girl who died at home on August 18. She had been born with a rare genetic condition called , which left her extremely vulnerable to infection, and the coroner concluded that measles killed her.
Neither baby was old enough to be vaccinated. The first dose of MMR is normally given at 12 months. Infants that young depend on two things for protection: antibodies passed from their mothers during pregnancy, which only work if the mother herself is immune, and a community where the virus is not circulating. In Lancaster County this summer, neither was guaranteed.
Then, on September 13, the Jefferson County coroner announced a third death. A 40-year-old woman died on September 12 of respiratory failure that her death certificate attributes to suspected measles along with chronic obstructive pulmonary disease and asthma, . She was unvaccinated, , had been exposed to several people with measles, and developed a fever and rash in the days before she died. Because she declined testing, the state health department is reviewing the case before deciding whether to add it to its official count. Jefferson County, in the western part of the state, has 26 confirmed cases this year and is one of the counties where the virus is spreading in the community.
It is worth pausing on these three lives. Two were babies who never had the chance to be protected. One was an adult with lung disease, the kind of person for whom a respiratory infection is most dangerous. None of them had the protection the vaccine offers, and each of them was infected because the virus was moving through their communities. Their vaccination status matters medically, because it explains how the virus reached them, but it is not a verdict on them or their families. It is a reminder that when measles finds people who are not protected, some of them will get very sick, and a few will die.
The rest of the numbers make the same point. So far, 124 people in Pennsylvania have been hospitalized, about 18 percent of all cases. Among children under 18, roughly one in seven has needed hospital care. Only four of the 676 cases occurred in people who were fully vaccinated, which is less than 1 percent, and none of those four were hospitalized.
Why Measles Finds the Gaps
Measles is the most contagious disease we know of. The virus hangs in the air for up to two hours after an infected person leaves a room, and of unprotected people who are exposed will become infected. Because it spreads so easily, communities need very high vaccination coverage, around 95 percent, to keep the virus from finding a foothold.
Pennsylvania has slipped below that line. The share of kindergartners with two doses of the measles, mumps, and rubella (MMR) vaccine fell from 95.5 percent in the 2020–21 school year to 93.2 percent in 2025–26, according to a of state data. Over the same period, exemptions from school vaccine requirements more than doubled, from 2.7 percent to 5.6 percent, driven almost entirely by religious and philosophical exemptions rather than medical ones.
A statewide average of 93 percent may not sound alarming. But averages hide pockets. In Lancaster County, home to the largest Mennonite community in the country and one of the largest Amish populations, are below the 95 percent threshold, twice as many as in 2019, and some classrooms are closer to 50 or 60 percent. Measles does not care about the state average. It cares about the room it is in.
What History Tells Us
Pennsylvania has been here before. In 1990 and 1991, a measles outbreak centered in Philadelphia , many of them in congregations that rejected vaccination and medical care. That outbreak was part of a national resurgence between 1989 and 1991 that sickened more than 55,000 Americans, and it changed vaccine policy: the country moved to a routine two-dose MMR schedule, and the outbreak helped spur the creation of programs to reach children who were falling through the cracks.
The lesson of 1991 was not that measles is unbeatable. It was the opposite. Within a decade of that resurgence, sustained two-dose coverage drove measles to elimination in the United States. The tools have not changed since then. Two doses of MMR are about 97 percent effective, and the protection lasts a lifetime for nearly everyone who receives them.
What Is Being Done, and What You Can Do
The state has been running pop-up vaccination clinics in affected communities, about 130 of them so far, and its own staff have given more than 6,500 doses of MMR this year. Statewide, , nearly double a typical month. Those are encouraging signs that many families are responding.
Because the virus is circulating, health officials have also adjusted the usual schedule. In counties with community transmission, babies as young as 6 months can receive an early dose of MMR, and children who have had one dose can get their second dose early, as long as at least 28 days have passed. Adults who are not sure whether they were ever vaccinated can safely get the vaccine or ask their doctor about a blood test for immunity. If you are unsure about your family's status, the simplest step is to check your records with your doctor, pharmacy, or local health department.
If you or your child develop a high fever with a cough, runny nose, red eyes, and then a rash that starts on the face and spreads downward, call ahead before going to a clinic or emergency room so staff can prevent exposing others in the waiting room.
The Bigger Picture
Nationally, the United States has confirmed as of September 10, already more than all of 2025 and the highest annual total in more than 35 years. About 95 percent of those cases were in people who were unvaccinated or whose vaccination status was unknown.
Pennsylvania's deaths are not yet reflected in the CDC's national count, which the agency says it will update once its own review is complete. Pennsylvania's outbreak is the largest piece of that national picture right now, but it is not unique. It follows the same pattern as South Carolina, Utah, and West Texas before it: a highly contagious virus, a community where vaccination has fallen, and a spread that outpaces the ability of public health workers to contain it one exposure at a time.
Measles is a preventable disease. Every one of the 676 cases in Pennsylvania this year, every hospitalization, and all three deaths were 99% preventable with a measles vaccine that has been in use since 1963. The two infants could not be vaccinated themselves; they were counting on the rest of us. That is the significance of this moment. Not that measles has changed, but that our protection against it has thinned in the places where it matters most, and the virus has filled the gap.