Measles erases immune ‘memory’ for other diseases

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Measles infections in children can wipe out the immune system’s memory of other illnesses such as influenza, according to a pair of studies1,2. This can leave kids who recover from measles vulnerable to other pathogens that they might have been protected from before their bout with the virus.

The findings, published on 31 October in Science and Science Immunology, come at a time when measles cases are spiking around the world. Globally, there were more measles infections in the first six months of 2019 than in any year since 2006, according to the World Health Organization.

The studies highlight the importance of measles vaccinations, says Michael Mina, an infectious-disease immunologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts, and a co-author of the Science paper.

The measles virus is highly contagious, and can lead to complications including pneumonia. And previous studies have suggested that the virus induces a kind of forgetfulness in the immune system, says Duane Wesemann, an immunologist at Brigham and Women’s Hospital in Boston. When people get an infection, their immune system creates antibodies to fight it off. Once the body clears the infection, special immune cells remember that pathogen and help to mount a faster defence if the virus or bacterium invades again.

The Science study is the first to show definitive evidence that measles can destroy this immune memory, Mina says.

Inducing amnesia

Mina and his colleagues analysed blood samples from 77 unvaccinated children from 3 schools in the Netherlands, taken before and after a measles outbreak in 2013. The team also collected blood samples from 33 children before and after their first vaccination against measles, mumps and rubella (MMR). The researchers analysed the kids’ antibodies using a test that measures the amount, and the strength, of antibodies against thousands of viral and bacterial substances.

Two months after the unvaccinated children recovered from measles, the team found that the virus had erased 11–73% of their antibodies against other bacteria and viruses. Although the reasons behind the high variability in antibody reduction are unclear, the finding shows that the virus alters previously acquired immune memory, Mina says. The kids who received the MMR vaccine showed no reduction in these antibodies.

Mina and his team also infected macaques with measles and monitored the animals’ antibodies against other pathogens for five months. The monkeys lost 40–60% of their antibodies against previously-encountered pathogens, suggesting that the measles virus destroys otherwise-long-lived plasma cells in the bone marrow that can produce pathogen-specific antibodies for decades, Mina says.

Measles also seems to wipe out immune cells that ‘remember’ encounters with specific bacteria and viruses, according to a separate, independent team that published the Science Immunology study. When the scientists analysed blood samples from the same group of unvaccinated children in the Science study, the researchers found that those ‘memory’ cells had disappeared in the children who had contracted measles.

Unexpected protection

The findings emphasize how the MMR vaccine protects against more than just measles, says Velislava Petrova, an immunologist at the Wellcome Sanger Institute in Hinxton, UK, who led the Science Immunology study. It also prevents longer-term damage to the immune system that can lead to a resurgence of other diseases, she says.

It’s possible to rebuild someone’s suite of antibodies against specific bacteria and viruses by exposing them to those pathogens again, says Stephen Elledge, a geneticist at Harvard Medical School in Boston, and a co-author of the Science study. But some kids could develop life-threatening diseases as a result. “Every time you're infected with a virus, that's rolling the dice,” he says.

As immunization rates drop in some countries because of anti-vaccine campaigns and infrastructure problems, the findings from the two studies could help officials to develop more effective vaccination policies, says Akiko Iwasaki, a viral immunologist at Yale University in New Haven, Connecticut. “For me, that would be making sure vaccination is mandatory for children in public schools,” she says.

Clinicians could also consider giving people with measles a booster shot of vaccines they have previously received against other diseases, especially in regions where measles outbreaks are common, such as in sub-Saharan Africa, says Mina.

However various governments choose to address vaccinations, it’s crucial that countries prevent measles outbreaks by maintaining high vaccination rates against the virus, Mina says. “We have to do our best to ensure that measles remains on the elimination radar.”

doi: 10.1038/d41586-019-03324-7
https://www.nature.com/articles/d41586-019-03324-7