Philadelphia health officials reported a measles case last week, marking the second known Pennsylvania infection this year after an earlier case was reported in Montgomery County. And though Western Pennsylvania has not reported any measles infections, the Allegheny County Health Department is urging residents to stay vigilant.

“We have alerted all of the providers in the area to be on the lookout for measles because there are a lot more cases in the U.S. this year than there have been in recent years,” said Dr. Kristen Mertz, an epidemiologist at the Allegheny County Health Department.

So far in 2025, there have been at least 301 confirmed cases reported in the United States, according to the Centers for Disease Control and Prevention. Most infections tie back to outbreaks in West Texas and New Mexico, where more than 280 cases have been reported. Two unvaccinated people — one in Texas and one in New Mexico — have died from measles-related causes.

Some experts suggest the case count could be higher. CDC data tends to trail behind real-time case counts due to reporting delays and not all cases of measles wind up in a doctor’s office, meaning medical providers may not capture every case.

Still, the 301 cases reported by the CDC late last week tops the total for all of last year. The CDC reported 285 measles cases in 2024, including an outbreak in a Chicago migrant shelter that sickened 60.

Most cases are in people who have not been vaccinated against the virus. Children ages 5 to 19 account for the largest share of cases at 42%, closely followed by young children under the age of five at 34% of cases. Most of those hospitalized are under the age of 5, according to CDC data.

The current measles outbreak is the country’s largest in six years. Measles cases were the worst in three decades in 2019 when 1,274 cases were reported. A California man died from measles complicated by meningitis during that outbreak.

So far this year, two people are believed to have died in connection to measles infections. Texas officials reported last month that an unvaccinated child died of the virus after being hospitalized in Lubbock. New Mexico is investigating the death of an unvaccinated Lea County resident who was discovered to have a measles infection postmortem.

What to look out for

Though measles is often associated with the red, blotchy rash that appears on the face before spreading downward over the rest of the body, the infection is caused by a virus that first infects the respiratory tract. Early symptoms include fever, runny nose, cough and red, watery eyes. Those symptoms don’t typically appear until 10 to 14 days after exposure.

“I think a lot of people just think of measles as a fever and a rash, but it does have these serious complications,” Mertz said.

Those complications can include pneumonia and encephalitis, which is the swelling of the brain. About 20% of unvaccinated people who get measles in the U.S. are hospitalized. A bout of measles can also wreak havoc on the immune system, making those who get sick more susceptible to other diseases.

There is no specific measles treatment, so medical providers often prioritize alleviating symptoms and preventing complications. Mertz said the best course of action is to prevent measles altogether with a vaccine.

If signs of measles appear, Mertz urges residents to wait before rushing to the hospital or their primary care doctor’s office. Because the virus is so contagious, special precautions need to be taken to avoid spreading the virus.

“You don’t want to just show up in an emergency room or an urgent care or a doctor’s office,” she said. “It’s always best to call ahead so that the facility can make arrangements for you to come straight to a room and not infect people in the waiting room because a lot of times that’s how measles spreads.”

Though no cases have been reported in Allegheny County, Mertz said the health department is prepared to act if one arises. The county will trace the history of an infected person to find potential exposure sites and warn those who may have been exposed — the county handled COVID-19 infections similarly during the height of the pandemic. Identifying people who may have been exposed to the virus is a “labor intensive” process, she said.

Measles begins as a respiratory infection and particles of the virus can linger in the air up to two hours after an infected person has left the room.

If someone has been exposed and has not gotten a vaccine, Mertz suggests getting the MMR shot within 72 hours of exposure. People may also seek antibody treatment for measles within six days of an exposure.

Declining vaccination rates

Measles is a highly contagious virus, but it is also vaccine preventable. Measles was declared eliminated in the United States in 2000 after a high percentage of people had received the MMR vaccine, which protects against measles, mumps and rubella. Doctors recommend two doses of the MMR vaccine, which usually protects people against measles and rubella for life. Immunity against mumps may decrease over time.

But vaccination rates have been declining over the last decade.

State-required vaccinations declined from 95% to 93% from the 2019-2020 school year to the 2022-2023 school year. To achieve herd immunity — which offers protections for those who cannot be vaccinated — research suggests that 95% of a population need to be vaccinated or protected by a prior infection.

Vaccination rates have dipped in certain communities around Pittsburgh, too. According to Allegheny County’s school immunization report last year, the percentage of students with all immunizations required for school entry was 94.6% in December 2023, down from 95.1% the year before.

Kids in public schools reported higher rates of vaccination than those in private, charter and parochial or religious schools.

Public schools — which account for nearly 83% of the total students in the county — reported 95.4% of measles immunity coverage for kindergarten students during the 2023 to 2024 school year. Kindergarteners are required to receive two doses of the MMR vaccine, which protects against measles, mumps and rubella.

But private and parochial schools reported lower vaccine uptake among their kindergarteners, all falling below the recommended threshold for herd immunity. Private schools in Allegheny County reported 93.9% coverage while charter schools reported 92.3% coverage. Parochial or religious schools reported the lowest percentage of kindergarteners immunized against measles at 89.5%.

Both measles cases reported in Pennsylvania this year were in children who traveled outside the U.S. and returned with an infection. Mertz urged families traveling abroad to ensure everyone is vaccinated against the virus to avoid infection and bringing it back home to others.

“Most measles cases we’re seeing are coming from people traveling,” she said. “And really the best prevention is to make sure you’re up to date on the vaccine.”