Pennsylvania's measles outbreak has surpassed 1,000 cases, state health officials announced Monday, marking the largest outbreak in any U.S. state in more than three decades. According to the Pennsylvania Department of Health, the state has recorded 1,004 measles cases with 198 hospitalizations and five deaths.

The outbreak began in late April west of Philadelphia and has shown no signs of slowing. Dr. John Goldman, an infectious disease expert at the University of Pittsburgh Medical Center, predicted the outbreak could continue for at least another three to six months, noting that while vaccination rates have increased, they remain insufficient to halt the epidemic's spread.

Nearly one-third of the measles cases have occurred in children. Among pediatric cases, 18 percent have required hospitalization. Dr. Evan Shirey, a pediatric infectious disease physician at Penn State Health Golisano Children's Hospital in Hershey, described severe complications including dehydration, hepatitis, and neurological damage. "One of the more common things that the measles virus can do is cause hepatitis or infection of the liver," Shirey said. "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 brain inflammation, resulting in severe and irreversible neurological damage.

The five deaths in Pennsylvania include a teenager with severe brain inflammation, a 40-year-old woman with a history of asthma, and two babies. One baby was a newborn whose mother went into labor a month early. Few details have been disclosed about the fifth death, other than that the person had not been vaccinated and lived in Lancaster County, where the bulk of measles cases are concentrated.

Lancaster County is home to the nation's largest Amish population, with approximately 44,000 residents as of 2025. While there is nothing in the Amish faith inherently opposed to vaccination, the community historically has had lower vaccination rates than the general population. According to an NBC News investigation, 88.5 percent of kindergartners in 2024 had the measles-mumps-rubella (MMR) vaccine. Health authorities emphasize that a vaccination rate of at least 95 percent is required to achieve herd immunity and protect against measles outbreaks. Dr. Goldman stated: "There's nothing special about Lancaster. The exact same thing could happen in any county in the country that has a large percentage of unvaccinated people."

The Pennsylvania outbreak surpassed South Carolina's previous record, which had recorded 997 cases earlier in 2026. That outbreak was contained within six months and has been described as the largest in approximately 30 years before Pennsylvania's current outbreak. State health officials credited a massive surge in vaccinations with bringing the South Carolina outbreak to a halt. In the northwestern corner of South Carolina, where the outbreak was centered, nearly 15,000 MMR vaccinations were administered during the outbreak, an 82 percent increase compared with the previous year. To date, the Pennsylvania Department of Health has administered just 8,843 MMR doses in response to the current outbreak.

The outbreak is not isolated to Pennsylvania. Ohio is experiencing a growing measles outbreak along the shared border, with 210 cases reported as of Thursday and 13 hospitalizations. Most cases are concentrated in northeastern counties including Geauga, Ashtabula, and Wayne, which have significant Amish populations. Additionally, New York Governor Kathy Hochul declared a disaster emergency on Monday due to measles cases in neighboring states and rural areas of New York, where more than 100 cases have been recorded this year. The executive order expands the pool of people authorized to administer measles vaccines to include paramedics, midwives, and others, and allows nurses to join doctors in ordering testing.

Nationally, the picture is dire. The United States is enduring its worst year for measles since 1991, with nearly 3,900 reported cases according to the Centers for Disease Control and Prevention. The nation has seen eight reported measles-associated deaths in the past two years—more than the combined total of reported deaths over the previous three decades. It's been decades since a U.S. state has seen an outbreak surpass 1,000 cases, stretching back to a multiyear outbreak in New York City in the early 1990s that infected more than 4,500 people. The nation eliminated the domestic spread of measles in 2000 by maintaining high vaccination rates, but those rates have fallen in recent years to below the 95 percent coverage needed to prevent outbreaks. In November, international health officials will meet to determine if the United States and Mexico have lost their measles-free status.

Health experts attribute the surge to declining childhood vaccination rates caused by parental waivers, healthcare access issues, and misinformation. Measles is highly contagious, spreading through breathing, coughing, sneezing, and contaminated surfaces. The virus can linger in the air for up to two hours, and up to nine out of 10 susceptible people will contract the virus if exposed.