One of the most important features of the human immune system is its incredible capacity for memory—the ability to remember a pathogen or other threat so that subsequent encounters take a lesser toll on wellbeing.
So it’s a pretty big problem when the body is forced to forget.
Reporting this week in the journals Science and Science Immunology, two teams of researchers have found that this is the modus operandi of measles virus. In addition to the disease brought on by the virus itself, measles can induce a kind of immune amnesia, leaving the body more vulnerable to infections it’s encountered before.
The findings underscore the urgent need for measles vaccination, which could protect people from more than the virus the treatment directly targets, the researchers say. In recent years, however, anti-vaccination movements have driven rates of vaccination down, prompting the number of measles cases to skyrocket on a global scale. More than 7 million cases and 100,000 deaths were reported in 2017, and numbers have continued to climb, Katrina Kretsinger of the World Health Organization, who was not involved in either study, told Debora MacKenzie at New Scientist.
“When parents say no to getting a measles vaccine, you’re not just taking a risk of your kid getting measles,” study author Michael J. Mina of Harvard Medical School told Denise Grady at The New York Times. “You’re causing them to lose this amazing resource of defenses they’ve built up over the years before measles, and that puts them at risk of catching other infections.”
When certain immune cells encounter a pathogen, they’re able to scan its surface and memorize it, storing away identifying intel that will help mount a stronger, faster response if the invader visits again. Often key to this process are the immune cells that produce antibodies—potent molecules that can neutralize bacteria, viruses, and other threats.
In the first study, a team of scientists led by Steve Elledge of Harvard Medical School analyzed blood that had been taken from 77 unvaccinated children in the months before and after a measles outbreak that hit the Netherlands in 2013. After an encounter with measles, 11 to 73% of antibodies that kids had generated against a wide array of viruses and bacteria—including those that cause herpes and pneumonia—disappeared.
When the researchers tested another group of 32 children that had been vaccinated against measles, mumps, and rubella, they found their antibodies intact.
Rather than destroying the antibodies directly, measles virus seemed to be targeting the cells that churned them out. Accordingly, the biggest drops occurred in children with the most severe cases of measles, Elledge told Grady.
The results of the second study, which analyzed the immune cells of 26 of the same unvaccinated children in the Netherlands, built on these results. Measles, they found, was capable of picking off several types of immune cells—many of which mature over time as young bodies are repeatedly exposed to, and recover from, infection. The onslaught, the researchers wrote, essentially rewound the body’s clock, leaving immune systems in an immature state that looked as though it had been “reset back to infancy,” study author Colin Russell of the University of Amsterdam in the Netherlands told MacKenzie.
Though researchers have known for years that measles can compromise the immune system, the two new studies are the first to dive into how the virus exerts its effects, which are “pretty devastating,” Jennifer Lighter, a pediatric infectious disease physician and epidemiologist who was not involved in either study, told Lena H. Sun at The Washington Post.
It’s possible for the immune system to recover from a measles attack, the researchers explain. But the body would probably need to be reexposed to the infections it’s forgotten, either naturally or through vaccination, to rebuild the memory it lost—a process that could take five years, study author Velislava Petrova of the Wellcome Sanger Institute and Cambridge University told Hannah Devlin at The Guardian.
It’s an argument for measles vaccination (which is a package deal when children are given the common measles, mumps, and rubella, or MMR, vaccine), Lighter told Sun. Some members of the population, like those who are immune-compromised, aren’t medically eligible for vaccination—but being surrounded by vaccinated people can still protect them.
Perhaps there’s a bit of irony to this: Our bodies must be taught to remember measles to avoid the risk of forgetting other pathogens. When first introduced in the 1960s, measles vaccinations prompted a plunge in infections—from measles, yes, but several other pathogens as well. Now it may finally be clear why: The vaccine, Lighter told Sun, “clearly has protection much greater than we previously recognized.”