Eliminating measles in the U.S. and the lost ‘memory’ of disease
Measles vaccines first became available in the U.S. in 1963. Since then, the vaccine has been modified, improved and combined with vaccines for the mumps and rubella viruses to form today’s MMR vaccine.
By 2020, U.S. cases of measles dropped dramatically, and the few cases reported nationally each year were mostly related to international travel and isolated incidents.
“This was the most, is the most, contagious infectious disease of humans, and we eliminated it. Amazing,” Offit said during a recent panel hosted by the Association of Health Care Journalists.
But the elimination of the disease had unintended consequences, Offit said.
“We largely eliminated the memory of measles,” he said. “I think people don’t remember how sick or dead that virus can make you.”
Because of that, some adults who grew up in recent decades never got vaccinated, he said.
“What you’re seeing now are people in their 20s, 30s and 40s who grew up at a time when this virus wasn’t circulating,” Offit said. “So, they’re not naturally infected. They’ve also, for whatever reason, not been vaccinated. So, you now have a fairly large population of susceptible adults.”
Immunization rates among school-aged children in Pennsylvania and across the U.S. have also steadily declined in recent years, national data shows.
Growing mistrust in medical providers and mainstream vaccination guidance, misconceptions on social media, and false claims about the dangers of vaccines have driven families to delay or reject shots altogether.
In Pennsylvania, pockets of unvaccinated residents in Amish and Mennonite communities who don’t use traditional health care systems are also bearing the brunt of the state’s ongoing measles outbreak, public health officials say.
The trajectory of Pennsylvania’s measles outbreak
Health care providers say they remain concerned about measles infections among Pennsylvania adults. About 1 in 5 people have become hospitalized, according to state data.
“We’re very quick to admit our children to the hospital for observation, rightfully so,” McHugh said. “As adults, we tend to not go until we’re really, really sick. I think that that’s just a general phenomenon among all of us and so, we’re seeing people who are admitted and pretty sick as adults.”
Health providers are also seeing an increase in measles infections among pregnant women, which have been linked to congenital measles, or a measles infection that is passed from a mother to her baby.
A state health advisory in October warned health care providers that babies born with measles infections could experience complications including delayed neurological conditions.
The positive news, McHugh said, is that measles transmission seems to be slowing down in local communities as more people become vaccinated and others develop immunity after surviving an infection.
“You run out of individuals who are susceptible to the infection,” she said. “That’s the natural course of what we would see from an epidemiologic perspective, is we would see a decreasing trend in the number of cases. Thankfully, we are starting to see that here in Pennsylvania. We’re hoping that that continues.”