Pennsylvania Measles Outbreak Tops 1,500 Cases as Infections Among Pregnant Women Hit Highest Level in Decades

HARRISBURG, Pa. — Pennsylvania's measles outbreak, the largest in the country, has passed 1,500 cases. Health officials are increasingly worried about infections among pregnant women, which pose serious risks to both mothers and babies.

The state Department of Health reported 1,505 cases as of Monday, up 18 from its previous update on Friday. The state recorded 73 new cases over the past week. Measles-related hospitalizations rose to 290, and the state has reported six measles-associated deaths this year. Cases have been confirmed in 45 counties.

People under 18 make up about a third of cases. Fewer than 1% of those infected were fully vaccinated, according to state data. Officials said only five cases involved vaccinated people.

The outbreak is centered in Lancaster County, home to a large Amish population, and the virus is actively spreading in suburban Chester County, west of Philadelphia. Health officials in Bucks County, north of Philadelphia, also confirmed a case this week. The state said it has not seen an outbreak of this size in 35 years.

As of Nov. 6, the health department had confirmed 97 measles cases in pregnant women this year, a spokesperson told ABC News. For comparison, Pennsylvania had 16 measles cases in total in 2025.

"The 97 cases of measles confirmed in pregnant women thus far in 2026 is the highest number of cases in that demographic in Pennsylvania in decades," the department said.

Measles during pregnancy can cause pneumonia, premature delivery, low birth weight, pregnancy loss and death, according to the CDC.

"You have to watch the mother fetus dyad so closely because of the risk of fetal death," said Dr. Sharee Livingston, an OB-GYN at UPMC Magee-Womens in central Pennsylvania. She said she has treated several pregnant patients with measles during the outbreak.

Babies born within about 10 days of their mother developing the measles rash are most at risk of being infected before birth, said Dr. Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia. Babies who survive face a higher risk of later developing subacute sclerosing panencephalitis, a rare and fatal brain disease.

The outbreak has already claimed the life of a new mother. Last week, the state reported that an unvaccinated 21-year-old woman from Jefferson County who had tested positive for measles died after complications following childbirth. It was the state's sixth measles-associated death this year. Her death certificate lists organ failure, postpartum hemorrhage, liver failure and suspected measles among the causes. Earlier in the outbreak, a 20-year-old Amish woman with leukemia also died after contracting measles.

Pregnant women cannot receive the MMR vaccine because it contains a weakened live virus. However, those who are exposed and not immune can receive immunoglobulin, an antibody treatment that can lower the risk of infection or reduce its severity.

"See your healthcare provider before you get pregnant," said Dr. Holly W. Cummings, chair of the Pennsylvania section of the American College of Obstetricians and Gynecologists. She urged women to check their immunity before pregnancy and said relatives around pregnant women and newborns should stay up to date on vaccines.

Doctors blame the outbreak on declining vaccination rates. The state's kindergarten MMR vaccination rate has fallen to 93.2%, down from 96.4% in the 2018-19 school year. That is below the roughly 95% level experts say is needed to prevent outbreaks.

"We had several decades without any measles transmission until our vaccination rates fell again," Dr. Evan Shirey, a pediatric infectious disease physician at Penn State Health, told WGAL.

About 200 health department staff are working with communities and health care providers to expand access to vaccines and accurate information, officials said.

Pennsylvania's outbreak is a major contributor to a national surge. The U.S. has recorded more than 5,100 measles cases this year, the most since 1991, as international health experts weigh whether the country has lost its measles-elimination status.