Pennsylvania’s health department today confirmed the state has recorded 1,004 measles cases this year, an increase of 106 cases in the past week.

More than 99% of people with measles in Pennsylvania have been unvaccinated, with just four cases in vaccinated people, according to the health department.

Pennsylvania has confirmed 198 hospitalizations, for a hospitalization rate of nearly 20%. 

Five people with measles have died, including two infants; a 20-year-old woman with leukemia who was being treated with chemotherapy, which suppresses the immune system; a 40-year-old woman with asthma and another underlying lung condition called chronic obstructive pulmonary disorder; and an 18-year-old who developed disseminated encephalomyelitis, a rare neurologic complication of measles with a high death rate. 

All were unvaccinated.

No other state has reported more than 1,000 measles cases in 35 years, when New York City alone confirmed 2,000 cases in 1991.

Nationwide, the Centers for Disease Control and Prevention (CDC) reported 3,887 measles cases as of October 2, a 6.2% increase from the previous week. 

The five deaths in Pennsylvania suggest the outbreak is much larger than reported, said Paul Offit, MD, director of the Vaccine Education Center at Children’s Hospital of Philadelphia.

Measles typically kills one to three people for every 1,000 people infected, Offit noted. With five deaths, that suggests there could be 5,000 or more cases in Pennsylvania.

It’s possible that milder cases are being missed. Unless people see a health professional, their measles infection is unlikely to be recorded, Offit said.

“Not everyone with measles goes to the doctor,” he said.

That’s especially true for Pennsylvania’s Amish community, which has been hard-hit by measles. Many Amish families prefer to care for sick children at home, rather than bringing them to the pediatrician.

Health department officials in South Carolina also have said that the state likely had more measles cases this year than the official count of 997. Doctors in South Carolina aren’t required to report measles-related hospitalizations, according to a report from ProPublica.

The United States declared measles eliminated in 2000, because high vaccination rates had stopped the virus from spreading from person to person. Although occasional travelers would enter the country with measles, the virus didn’t spread widely.

Offit and many other health experts predict the United States will lose its elimination status next month, when the Pan American Health Organization meets to review the spread of measles outbreaks in the country.

Pennsylvania healthcare providers vaccinated 53,000 people with the combined measles, mumps, and rubella (MMR) shot in September, more than twice the typical number of vaccinations, according to the state health department.

Those efforts may not be enough to stop the spread of measles, one of the most contagious of all viruses, Offit said.

“Measles is now endemic in the United States,” he added. “We’re going to be seeing measles outbreaks for years.”

The Pennsylvania measles outbreak is unusual because of the large number of infected adults, Offit said. Before the measles vaccine was available, most people infected with measles were under 5 years old, and virtually everyone was immune by age 15. People born before 1957 are considered protected from measles because of the very high likelihood that they were infected.

Only 32% of reported measles infections in Pennsylvania were diagnosed in children under 18 years old, according to the state health department. The largest numbers of cases in the state have occurred in people ages 25 to 49.

Offit notes that all five measles deaths were either in adults or in newborns who caught the infection from adults. That’s very different from the measles outbreaks of the midcentury, when the virus mostly spread from child to child.

The US measles outbreak this year is the largest since 1991, when the nation was in the grips of a massive measles epidemic. That outbreak led to 9,643 measles cases in 1991. US officials recorded 27,786 infections in 1990 and 17,840 cases in 1989. 

The 1989-1991 measles epidemic has been blamed on budget cuts to vaccination programs and on national recommendations calling for children to receive just one dose of measles vaccine. In response, an influential advisory panel to the CDC recommended two doses of MMR vaccine in 1989.

Today’s high number of measles cases are likely due to low vaccination rates in certain communities, experts say.

Because measles is so contagious, communities need to vaccinate 95% of children to prevent outbreaks. But measles vaccination rates among kindergarten children have fallen from 95.2% in the 2019- 20 school year to 92.5% in 2024- 25, with much lower levels in certain communities. 

In New York state today, measles outbreaks prompted Gov. Kathy Hochul to declare a state disaster emergency. New York health officials have confirmed 108 measles case, including many in rural communities with low vaccination rates.

The declaration allows New York to “respond more swiftly to the outbreak and allows healthcare professionals to take additional steps that will help get more New Yorkers vaccinated and tested,” the governor’s office said.

The office said the emergency declaration is “in response to the growing number of measles cases across rural areas of New York and neighboring states,” which include Pennsylvania.