Measles wipe immune system's memory of other illnesses, studies find

Lindsey Wasson  Reuters

Lindsey Wasson Reuters

Measles infections eliminate the immune system's memory of infectious diseases, resetting the human immune system to a baby-like state and increasing vulnerability to other unsafe infectious diseases like diphtheria, tuberculosis, and the flu, according to two new studies published today. But the results are another good reason to immunize children against the virus, the studies' authors and other infectious disease experts say.

When the measles vaccine first became available in the 1960s, something curious happened: Scientists began to notice a drastic drop in the number of children dying from other infectious diseases as well.

It underlines the importance of getting the jab, especially with cases of measles on the rise around the world.

Contracting measles doesn't just make you feel lousy and put you at risk of potentially life-threatening complications, it can also cripple your immune system for years.

The researchers used new technology that can detect hundreds of antibodies against different viruses in blood. Measles infection erases big sections of the text, an effect sometimes called immune amnesia. "It's much more risky to children who get it, not only when they get it but for years afterwards". So, while people who come down with measles are protected from future bouts of that virus, they seem to be left unprotected from other, previously known pathogens and ill-equipped to respond to new ones.

The results of a separate study, also out today, from Harvard University in America are published in the journal Science.

Initially, the theory was that the vaccine was somehow bolstering the immune system.

For this research, the two teams looked at a group of unvaccinated people in the Netherlands to find out what measles does to the immune system.

What they found was that after measles, previously healthy kids lost on average about half - and as much as 73% - of their overall antibody diversity.

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The blood samples were collected before and after infection to compare how their immune system changed. The body can rebuild those defenses - but it could take years. B-cells keep building these antibodies even after the pathogen clears, so the body "remembers" the disease if it ever returns. The virus killed off B cells specific to other pathogens, allowing new, measles-specific memory B's to replace them.

"[My co-author Rik de Swart] went into this community in the Netherlands with these unvaccinated Dutch Orthodox Protestant members and asked them if he could enroll them in a clinical study", says Michael Mina, the study's first author.

Together, both studies provide support for the idea that infection with measles can and does compromise the body's immunological memory. It takes time for antibodies to fade from the blood, he says. Even the US, where most children are immunized, has seen a resurgence fueled by outbreaks in unvaccinated communities that in turn threaten people too young or sick to be immunized.

Measles is far more harmful than scientists once suspected.

For people vaccinated decades ago, the amount of measles antibodies in the blood might be too low for VirScan to spot.

The study "quite convincingly showed that this immune damage is likely the actual antibodies disappearing", Wesemann told Live Science. Since then, measles has resurged, often tearing through unvaccinated or under-vaccinated communities. During the Science study, some children quickly regained new antibodies to fight off staph infections, influenza and adenoviruses, the family of viruses that cause sore throats and pneumonia. "Ultimately, the conclusions that can be drawn are very similar: Infection really skews the naive repertoire, and you could expect that that would have long-term, downstream consequences on immune memory", Mina says. Questions also remain about why some kids lose more antibodies to measles than others, and how shifts in white-cell diversity affect survivors in the long term, he said.

Measles is a risky virus, and before the introduction of the vaccine, it infected 3 to 4 million children, killing between 400 and 500 annually in the United States. But unlike infection, inoculation does not blunt the body's ability to build antibodies against other pathogens - the Science study shows this incredible feat in action. "You get the best of both worlds with the vaccine", Wesemann says.

The researchers confirmed that finding by infecting flu-vaccinated ferrets with a measles-like illness.

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