Pennsylvania’s measles outbreak is closing in on 900 confirmed cases as health officials expand vaccination efforts across communities hit hardest by the highly contagious virus.
According to the Pennsylvania Department of Health, the state had confirmed 890 measles cases across 39 counties as of September 25, including 55 new cases reported since September 23. State officials also reported 173 hospitalizations and four measles-associated deaths connected to the outbreak.
“While daily numbers fluctuate,” the department said, “tracking these trends provides Pennsylvanians and health care providers with visibility into community transmission across the Commonwealth and helps inform the department’s ongoing response.”
The Pennsylvania measles outbreak has accelerated significantly during September. According to the Pennsylvania Department of Health, the state had 577 confirmed cases across 37 counties on September 4. By September 23, that figure had climbed to 835 cases across 39 counties, according to a separate state health update. Two days later, officials announced another 55 cases, pushing the total to 890.
Vaccination status remains a major factor in the outbreak. The Pennsylvania Department of Health reported that only four of the state’s 890 confirmed cases involved people who were appropriately vaccinated for their age, representing less than 1 percent of the total. In an earlier state update, health officials identified those four breakthrough infections as three adults and one child living in Centre, Jefferson, Lancaster and Lycoming counties.
The outbreak is unfolding as measles cases rise nationally. According to the Centers for Disease Control and Prevention, 3,659 confirmed measles cases had been reported in the United States in 2026 as of September 24. The CDC said cases had been reported across 47 jurisdictions.
The national total has already surpassed recent years by a wide margin. The CDC reported that 2025 ended with more than 2,200 measles cases and three confirmed deaths. The agency has said measles cases have been increasing since early 2025 following several large outbreaks.
Pennsylvania and federal health authorities have not reported the same death count for 2026. Pennsylvania officials have classified four deaths as measles-associated, while the CDC’s September 25 national update listed one death nationwide.
“This number is subject to change; C.D.C. will update its reporting as additional information becomes available and relevant reviews are completed,” the CDC said.
The CDC also said it is working with the Council of State and Territorial Epidemiologists to develop a standardized definition for deaths caused by measles, with the goal of making classifications more consistent across jurisdictions.
Meanwhile, Pennsylvania officials have dramatically increased vaccination outreach since the outbreak began in late April. According to the Pennsylvania Department of Health, state health officials have “administered more than 5,300 M.M.R. vaccinations at 165 pop-up vaccination clinics in the affected communities.”
Dozens of additional clinics are planned for the coming weeks and months “based on community interest and need,” according to the department. State health center employees have administered more than 7,900 MMR vaccine doses across Pennsylvania during 2026, the agency reported.
The surge in vaccinations has become particularly noticeable as cases have climbed. According to the state’s September 23 update, Pennsylvania health care providers administered more than 38,000 MMR doses during the first three weeks of September. The state said a typical month sees roughly 25,000 doses administered.
Measles can spread rapidly among people without immunity. According to the CDC, the virus spreads through the air when an infected person coughs or sneezes, and someone can become infected simply by entering a room where a contagious person had been up to two hours earlier. The agency estimates that as many as nine out of 10 susceptible people who have close contact with someone carrying measles can become infected.
Symptoms generally emerge seven to 14 days after exposure and can include a high fever, cough, runny nose, red or watery eyes, and a rash, according to the CDC.
Although many people recover, the infection can cause serious complications. The CDC’s guidance on measles complications states that about one in five unvaccinated people in the United States who contract measles require hospitalization. Potential complications include pneumonia and encephalitis, or swelling of the brain.
Health officials continue to emphasize vaccination as the primary way to prevent infection. According to the CDC’s current vaccine recommendations, two doses of the MMR vaccine are approximately 97 percent effective at preventing measles, while one dose is approximately 93 percent effective.
Pennsylvania’s Department of Health said the “best protection against measles remains getting fully vaccinated,” adding that the M.M.R. vaccine “boosts a person’s immune system and provides 97 percent lifetime protection.”
With hundreds of Pennsylvania residents already infected and new cases continuing to emerge, state officials are keeping vaccination clinics active while tracking transmission across the 39 counties where cases have been confirmed.
