Pennsylvania measles cases reach 1,004, largest US outbreak in decades

Pennsylvania's measles outbreak reached 1,004 confirmed cases on Monday, the largest in the United States in three decades, with 198 people hospitalized and five deaths the state classifies as measles-associated.

The Pennsylvania Department of Health reported the total in its Monday update, covering 39 of the state's 67 counties. The count passed South Carolina's outbreak earlier this year, which topped out at 997 cases and was contained within six months, NBC News reported. Pennsylvania's outbreak shows no sign of slowing.

Lancaster County is the center of the outbreak, with 391 confirmed cases. The county is home to the nation's oldest Amish and Mennonite communities, both of which have under-vaccinated populations, Al Jazeera reported. The outbreak began in the Lebanon County area in late April, then spread across much of the state.

The toll on children

Nearly a third of Pennsylvania's cases have been in children, and 18% of those pediatric patients have required hospitalization, NBC News reported. Dehydration has become a common problem, particularly among babies and younger children, said Dr. Evan Shirey, a pediatric infectious disease physician at Penn State Health Golisano Children's Hospital in Hershey. Doctors are also seeing young patients with liver problems.

These children will feel very sick, very nauseous, with abdominal pain and vomiting, and they can't take a bottle or can't keep food or liquid down.

Some children have developed encephalitis, or inflammation of the brain, with severe and irreversible neurological damage, Shirey said. He described patients who are disoriented and confused and cannot recognize their own mother. Others have developed secondary bacterial infections.

Five people in the state have died. They include a teenager with severe brain inflammation and a 40-year-old woman with a history of asthma, NBC News reported, and two babies, one a newborn whose mother went into labor a month early. Department data lists the adults among the dead as an unvaccinated 18-year-old and an unvaccinated 40-year-old, and the two infants as too young to have received the MMR vaccine.

A dispute over the count

Pennsylvania counts five measles-associated deaths. The CDC's national tally included two measles-related deaths, and the agency did not identify where they occurred, Al Jazeera reported on September 30. The gap has become a dispute between Governor Josh Shapiro and US Health Secretary Robert F. Kennedy Jr. over how a measles death is classified.

The state applies the measles-associated label when a person with a confirmed measles infection dies within 30 days of developing symptoms, unless the death resulted from an unrelated event.

Pennsylvania announced its first two measles-associated deaths in August, the first measles-related deaths recorded in the state in 35 years, and confirmed infections have more than doubled since.

Kennedy, a vaccine skeptic, has accused Shapiro of politicizing the deaths and initially questioned whether the two August deaths were linked to measles. He made the claim in a post on the social media platform X on August 26.

The announcement appears to have been premature, and the deaths may even have been altogether fabricated by one of the Governor's hopeful staffers.

Epidemiologists told Al Jazeera that counting measles-associated deaths has long been a standard used by the World Health Organization and the CDC, and infectious disease experts have warned that the classification dispute puts the agency at odds with that approach.

What the state has not said

The fifth death was announced on September 30, when the health department said an unvaccinated Lancaster County resident who had tested positive for measles had died and that the death had been reported to the CDC. The department released no further details about the person, and ABC News reported on October 5 that the individual's age remained unclear. It was the third measles-associated death in Lancaster County this year.

Fewer than 1% of the state's cases have been in people fully vaccinated with the MMR vaccine, according to the health department. Only four cases have been in people appropriately vaccinated for their age under state guidelines. All five deaths have been in unvaccinated people.

The outbreak counted 84 cases by June 26, 393 by August 25 and 693 by September 14, across 38 counties. The total reached 903 on September 28 and 1,004 a week later.

Pennsylvania recorded 12 measles cases in the first quarter of 2026, 83% of them in young children and nearly all unvaccinated, with one hospitalization, according to the National Foundation for Infectious Diseases. By the end of March, at least a week had passed with no new cases. Three cases in Lebanon County then prompted a May 1 state advisory, and by May 6 eleven residents had been diagnosed, ten of them unvaccinated.

The vaccination response

More than 53,000 MMR doses were administered statewide in September, more than twice the number given in a typical month, according to the health department. Department staff have given more than 8,800 doses this year, about 3,500 of them in August and more than 2,500 in September. State and local health departments have brought pop-up vaccination clinics and home visits to communities, the National Foundation for Infectious Diseases said.

Pennsylvania's request for federal help

Pennsylvania asked the CDC in September for an Epi-Aid investigation, a federal resource used in urgent disease outbreaks, Al Jazeera reported on September 30. In a statement to ABC News after the fifth death, the CDC said it had not received a formal Epi-Aid request from Pennsylvania, and that it was ready to deploy epidemiologists if one came.

An Epi-Aid is a rapid, short-term field investigation of what the agency calls an urgent public health problem, and it can supply extra staff for rapid response and help build epidemiologic capacity. The CDC said Texas, South Carolina, Virginia, Kansas, New Mexico and Wisconsin had requested Epi-Aids and worked with federal teams to bring their outbreaks under control. It also said it was deeply saddened by another death in Pennsylvania.

The national picture

Measles cases in the United States have surpassed 3,800 this year, confirmed in 45 states and Washington, D.C., according to CDC data, the highest national total since 1991. The Johns Hopkins US measles tracker put the figure at 4,020, a count cited by the National Foundation for Infectious Diseases, which said Pennsylvania accounts for nearly a quarter of US cases.

Kindergarten MMR coverage nationally was 92.4% in the 2025 to 2026 school year, down from 95.2% in 2019 to 2020, before the COVID-19 pandemic, CDC data shows. Epidemiologists put the threshold for community immunity at 95%.

A Reuters/Ipsos poll conducted in September 2026 found that 76% of Americans considered the MMR vaccine safe for children, down from 84% in a comparable Reuters/Ipsos survey in May 2020.

Measles is among the most contagious viruses known, and up to nine in 10 unvaccinated people exposed to it become infected, with each infected person able to transmit the virus to 12 to 18 others, the National Foundation for Infectious Diseases said. The Pennsylvania counties reporting no cases have MMR vaccination rates above 95%.

The months ahead

Dr. John Goldman, an infectious disease expert at the University of Pittsburgh Medical Center, told NBC News he would bet the outbreak runs at least another three to six months. Vaccinations have increased, he said, but not enough people are being vaccinated to stop it.

Pennsylvania reported 106 new cases in the most recent week and two-thirds of its cases are now in adults, the National Foundation for Infectious Diseases said on October 6. The outbreak has reached 39 of the state's 67 counties.