As the U.S. surpasses 1,000 confirmed measles cases, what does that mean for Pa.?
By Anya Sostek / Pittsburgh Post-Gazette
Confirmed measles cases for the year ticked over 1,000 nationally on Friday — the latest milestone in one of the largest measles tallies in decades.
Thus far, Pennsylvania has played a minuscule role in the overall count. The 15 confirmed cases in the state in 2025 are more than have been reported statewide in recent years, but represent a small fraction of the cases reported nationally.
That said, steady drops in vaccination rates have schools in Allegheny County and Pennsylvania falling below the herd immunity rate of 95% vaccinated for measles, meaning that the area could be vulnerable to future outbreaks.
Data from the Allegheny County Health Department shows significant drops in measles vaccinations among kindergarteners since the start of the COVID-19 pandemic, particularly in charter and religious schools.
In the 2019-20 school year, 94.7% of charter school kindergarteners and 94.6% of religious and parochial school kindergarteners had received two doses of the MMR vaccine, which protects against measles, mumps and rubella. Data recently released by the county for kindergarteners in the 2024-25 school year shows those figures at 89% for charter schools and 88.6% for religious and parochial schools.
“This is well below herd immunity and could produce outbreaks,” said Mark Roberts, distinguished professor of health policy and management and director of the Public Health Dynamics Lab at the University of Pittsburgh School of Public Health.
The overall rate for MMR vaccinations in kindergarteners in Allegheny County — including students in public and private schools in addition to charter and religious ones – was 93.9% for the 2024-25 school year. That number is down from 97% for kindergarteners in the 2019-20 school year, and falls below the 95% herd immunity figure.
In 2019, Dr. Roberts released a simulator built by his team at Pitt that demonstrated what happens to hypothetical measles outbreaks if vaccination rates fall. That simulator, called FRED, predicted that one case under 2019 vaccination rates in Allegheny County could cause an outbreak of 25 cases. If those school vaccination rates dropped by 2%, that outbreak would grow to 67 cases, according to the simulator. A 4% drop from the initial rate could result in 922 cases.
Measles is a highly contagious illness that often begins with a fever, runny nose, cough and red eyes. A few days later, a distinctive rash may appear, along with a high fever.
While most people recover from measles, it can cause serious complications such as pneumonia, blindness, brain swelling and even death. Before the measles vaccine became available in 1963, the U.S. had about 400-500 measles deaths per year, with 48,000 people hospitalized annually, according to the U.S. Centers for Disease Control.
The vaccine largely eradicated the disease in the U.S. and, in 2000, the disease was declared to be eliminated, meaning no continuous transmission of cases for more than a year.
In the years since, however, there have been scattered outbreaks. Friday, the CDC declared 1,001 confirmed cases for the year, with the amount of unconfirmed cases expected to be much larger.
“It hasn’t been common for two decades,” said Faina Linkov, an epidemiologist and associate professor in the John G. Rangos Sr. School of Health Sciences at Duquesne University. “However, recently it started to come back because the public’s trust in preventative measures such as immunization have been in question.”
In 2025, 93% of the confirmed measles cases nationally came from 14 separate outbreaks, with an outbreak defined as three or more related cases.
More than 700 cases are tied to an outbreak that began in West Texas, in a Mennonite community with low vaccination rates. In Texas alone, 92 people have been hospitalized and two school-aged children have died from measles.
Another outbreak occurred in Erie County, with at least five cases tied to an unvaccinated child diagnosed with measles on March 30. Erie County has had a total of eight measles cases this year, making up more than half of the state total. Public officials in Erie believe that the outbreak is contained.
According to the CDC, 13% of the 1,001 confirmed cases have resulted in hospitalizations. Of those cases, 96% are unvaccinated or have an unknown vaccination status, 2% have received one MMR shot and 2% are considered fully vaccinated with two MMR doses. Three total deaths have been reported.
“There is only one factor — the loss of vaccination to levels below herd immunity,” said Dr. Roberts. “Essentially nothing else matters.”
Measles is one of the most contagious common diseases, said Dr. Roberts, noting that the contagiousness is traditionally measured by the number of people who would be infected by one person with the disease if no one in the population was immune. For measles, that number is 18, in contrast with 1.5 for influenza and between 2 and 3.5 for COVID-19.
Herd immunity is the level of immunization required for it to be difficult for a disease to spread.
Because measles is so contagious, the herd immunity is high, at 95%.
Statewide, Pennsylvania is near those levels – at 94% of kindergarteners vaccinated. That figure is likely helping Pennsylvania weather this outbreak, along with relatively low levels of international travel compared to some other states, said Dr. Linkov.
But without an increase in vaccination rates, it’s likely that Pennsylvania could see outbreaks in the future.
“People need to be encouraged to be vaccinated,” she said. “In general, we need to be doing something that fights misinformation and disinformation on media channels. Right now, people do not get their information from the CDC — they get it from their friends or social media or TikTok, and I’m not sure that those sources of information are sufficient to protect us.”