Measles, a highly contagious disease that was at one point believed to be largely eradicated in the United States, has seen an increase in cases over the past year.
Among the most recently diagnosed cases of measles are several instances in New Jersey in mid-February and a confirmed case in Montgomery County over the weekend, marking the first instance of a measles infection in Pennsylvania for 2025.
Thus far, all of the cases in New Jersey and Pennsylvania have been linked to international travel.
A statement from the Pennsylvania Department of Health reads that “there is no immediate risk to the general public at this time, as 94% of Commonwealth residents are vaccinated against the measles virus.”
“According to the CDC, two doses of the measles, mumps, and rubella (MMR) vaccine is 97 percent effective against measles,” the statement says.
The extremely high rates of vaccinations are particularly important against measles, according to Dr. Jessica Ericson, a specialist in pediatric infectious diseases at Penn State Health in Hershey.
That’s because of how easily it can spread among those who aren’t vaccinated.
“Measles is really the most contagious illness that we know of,” Ericson said. “It’s more contagious than Ebola. It’s certainly more contagious than the flu.”
The elimination of measles was an “amazing point” for our national health, Ericson said Monday. “And I think that we’re in grave danger of that not being the case, and that measles is really going to come back and be an illness that parents have to worry about for their young children.”
Ericson added that measles is “much less of a discriminating virus than something like influenza, where it’s just the really young and the really old who get sick.”
School-age children can be badly stricken by the measles, she said, and potentially lead to infections in organs like the brain and lungs.
“All of those problems can lead to death in healthy children,” Ericson said. “But the other thing that measles does is it causes what we call immune paralysis. So for the month or two after a child has had measles, their immune system doesn’t work very well, so they’re almost like a cancer patient.”
This leaves a measles patient open to infections such as pneumonia or meningitis, she said, which can also have potentially deadly complications.
While most Americans are vaccinated against measles, and that vaccine is highly effective, infection with measles can potentially be fatal.
Recent outbreaks include a case in which an unvaccinated child in rural West Texas died from the disease. That case is part of the largest outbreak of measles in Texas in 30 years, with 158 cases spread across nine counties.
When enough of a population is vaccinated, the chances of a disease spreading drops significantly. But as measles is so highly contagious, Ericson said that vaccination rates need to be around 95% of a community’s population for them to be safe.
And while the average statewide is close to that number, she said, that means some communities across the state will be higher, and some will be lower — leaving them even more vulnerable.
“We’re going to have pockets where groups of families, groups of friends, or there may be communities that are quite a bit less than that 95%,” Ericson said. “Should they end up having one person from that community run into the measles virus, that community would be at increased risk.”
Fortunately, if you’ve been vaccinated against measles, the odds are very good that you will be fine and have no need for booster shots.
“It’s really just if you’ve had a bone marrow transplant, or if you got your measles vaccine during the ’60s,” Ericson said. “There’s really just this little window of folks who who might benefit from from getting another vaccine. Most people who’ve had the vaccine don’t need to worry about getting any more.”
Warning signs of measles are similar to several other respiratory viruses, including cough, runny nose and fever. Sores in the mouth and a reddish rash are more telltale signs.
If you or someone near you is concerned that they may have the measles, Ericson said to call a doctor before just going in to visit. Measles can be spread by airborne particles hours after an infected person was in a room, meaning that a single infected patient could make an entire waiting room unusable for an entire day as a safety precaution.
For more information on measles and tracking cases in Pennsylvania, check the Department of Health’s updates here.