How measles wipes out the body's immune memory

Maricruz Casares
Noviembre 8, 2019

Impressive new research from an global team of scientists has effectively verified a long-held hypothesis called immune amnesia, demonstrating how infection by the measles virus can quite literally remove pre-existing immune system protections, leaving a person vulnerable to other infections for several years.

Researchers already knew that measles affects the immune system, but these two studies confirm for the first time the mechanisms of immune amnesia. About 20 percent of people in the USA who get infected with measles require hospitalization, according to the CDC, and some experience well-known long-term consequences, including brain damage and vision and hearing loss.

Now researchers say measles vaccination not only controls measles, but it also protects the immune system from losing its ability to suppress other infections.

The "Mina" study of 77 children, found that unvaccinated children who had measles lost between 11 and 73 per cent of their antibody repertoire two months after infection. The researchers then compared these samples with the blood of 115 uninfected children and adults using the VirScan system, a tool that detects antiviral and antibacterial antibodies in the blood. Without them, the body is vulnerable to pathogens such as the influenza virus or pneumococcal bacteria that cause ear infections.

The lead author and professor of genetics at Brigham and Women's Hospital and Harvard Medical School in Boston say that the measles virus is furthermore deleterious than previously thought. However, precisely how post-measles immune suppression unfolds in humans is unknown.

Two studies published today have revealed how this dampening effect, called "immune amnesia", impacts un-vaccinated children.

To find out what measles does to the immune system, researchers looked at a group of non-vaccinated people in the Netherlands - from a non-vaccinating Orthodox Protestant community.

The discovery that measles depletes people's antibody repertoires, partially obliterating immune memory to most previously encountered pathogens, supports the immune amnesia hypothesis.

The findings help explain why countries that start to vaccinate children against measles see pediatric death rates drop substantially, beyond just the decrease that would be expected with the prevention of measles deaths.

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These recent outbreaks have been put down to the growth of the anti-vaccination movement, which has spread via social media and discourages parents from immunizing their children against measles and other diseases.

In one study, they sequenced antibody genes from 26 children, before and then 40 to 50 days after measles infection, and found that specific antibodies that had been built up against other diseases had disappeared from the children's blood.

Since 2018, however, the paper explains that reduced vaccination alone has led to a almost 300 percent increase in measles infections, and the impact on herd immunity could extend far beyond this one disease. After the initial phase of the infection, a subset of the cells remains in the body, pumping out antibodies to guard against future attacks - a concept known as immunological memory.

Peoples' immune systems are like blackboards onto which immunological experiences - the antibodies they developed after contracting the flu or getting vaccinated against chickenpox and polio - are written.

"Our study has huge implications for vaccination and public health as we show that not only does measles vaccination protect people from measles, but also protects from other infectious diseases".

"Every time we see a pathogen, our immune system recognizes this pathogen, builds immunity to it and then stores it in the form of immune memory", explains Velislava Petrova, a postdoctoral fellow in immunogenetics at the Wellcome Sanger Institute in the United Kingdom and first author of the report published in Science Immunology. The findings also serve as a reminder that this year's record-breaking measles outbreaks in the USA will have lingering effects, Schaffner added. "It's like taking somebody's immune system and rewinding time, putting them at a more naïve state", Mina says.

"You can be in an accident and you could have a head injury and you could lose your memory", Elledge said. "We show that measles directly causes the loss of protection to other infectious diseases". "If you don't get vaccinated against measles, you are running that risk". But two months after recovering from measles, the children had lost on average 20 percent of their usual antibody mix.

Virscan, the technology that enabled this research, was unveiled just weeks after Mina's 2015 paper showing that children became more susceptible to other infections after acquiring measles.

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