Measles remains a danger to health even years after an infection

The measles outbreak in Texas and New Mexico is now close to 300 reported cases, surpassing the total number of cases in all of the U.S. in 2024.

The outbreak is happening in remote, rural areas. There have been a few isolated cases reported in 13 other states — not related to the Texas outbreak. The Centers for Disease Control and Prevention says the nationwide risk remains low and that vaccination is the key to prevention.

Still, doctors say it's a good time to remember how dangerous and long-lasting the health consequences of measles can be.

Dr. Alex Cvijanovich has been a practicing pediatrician for more than 20 years. She says she's still haunted by the memory of a teenage boy she treated at the start of her career in Utah.

The boy had contracted measles as a 7-month-old, when he was too young to be vaccinated. "He got the virus from a child in his neighborhood who was unvaccinated," says Cvijanovich, who now practices in New Mexico.

It was a relatively mild case of measles, and the infant recovered. She says he grew up to be a healthy, bright kid — an honor student.

Then in middle school, he started to develop troubling symptoms. "He started getting lost between classes, lost like he couldn't find what class to go to next," Cvijanovich says.

Worried, the teen's parents took him to a series of doctors to figure out what was wrong, until a pediatric neurologist finally suspected a condition called subacute sclerosing panencephalitis, or SSPE. It's a degenerative neurological condition that typically develops seven to 10 years after a measles infection. It is almost always fatal. Cvijanovich was part of the hospital team that confirmed the diagnosis.

"The problem is that there is no treatment for it," she says. "And he basically became more and more incapacitated over time."

Some 18 months after his initial diagnosis, she says, the teenager died.

SSPE was once considered quite rare. But Dr. Adam Ratner, a pediatric infectious disease specialist in New York City who wrote a history of measles, says data from outbreaks in the U.S. over the past several decades suggests that may not always be the case.

"It turns out that in some age groups, especially in kids under about age 2, it's much more common than we thought," Ratner says.

For example, a review of measles cases in California found that, between 1988 and 1991, SSPE cases occurred as frequently as 1 in every 1,367 cases in unvaccinated children under age 5. Another study that looked at U.S. outbreaks between 1989 and 1991 put the rate of SSPE at roughly 1 out of every 4,600 measles cases.

Vaccination prevents not just SSPE, but also other serious complications that measles can cause — including pneumonia and severe brain swelling.

And there's a common consequence from measles infection you might not know of: It can erase your immune memory.

"Not only does your brain have a memory, but your immune system has a memory of all the pathogens it's encountered in the past," says Stephen Elledge, a professor in the genetics department at Harvard Medical School who studies how the immune system responds to pathogens.

Elledge says your immune system holds on to those memories, so the next time it encounters a virus, it knows how to fight it. But measles can destroy the cells that retain those memories.

"And when you lose that memory, then you're no longer immune to that particular pathogen," he says. "So the next time you get it, you've got to fight that battle all over again."

This effect is called immune amnesia. Elledge says it happens to some extent with every measles infection, though its severity varies widely.

"So whenever you get measles, you lose some of your immune memory. And the more severe your case of measles is, the longer it lasts, the more of your immune system is destroyed."

In one study, Elledge and his colleagues found that unvaccinated children had lost between 11% and 73% of their antibodies, which recognize and neutralize viruses and bacteria. 

Other research suggests it can take two to three years for the immune system to recover. And in the meantime, kids might be left vulnerable to infection from other diseases, including ones they had previously been immune to.

Researchers say immune amnesia helps explain one phenomenon that was documented after the introduction of the measles vaccine in the 1960s: Deaths from other childhood diseases dropped dramatically. Even deaths from diseases like pneumonia and diarrhea were cut in half.

Ratner says as routine childhood vaccination rates fall, the U.S. is likely to see more and larger measles outbreaks. "There's no doubt that we will in the future see the long-term consequences of measles," he says.

But he says we have a safe and powerful tool to prevent those consequences — vaccines.
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