The reason why measles causes long-term damage to the immune system, leaving people vulnerable to other infections, has been revealed in a new study.
The findings of the research, published in the latest edition of Science Immunology, could have enormous implications for public health, researchers say.
In fact, the researchers warn that the effect of a newly limited immune system in some children was so strong that the result is similar to being given powerful immunosuppressive drugs.
Even though it was known that measles weakens the immune system, it was not known how.
The researchers, from the Wellcome Sanger Institute and University of Amsterdam, plus other collaborators, show for the first time that measles resets the human immune system back to an immature baby-like state in both humans and ferrets. This means that the body has limited ability to respond to new infections.
The team looked at a cohort from three schools in the Netherlands, none of whom had been vaccinated. Blood samples were taken from healthy volunteers and they were followed-up for repeat sampling after a measles outbreak in 2013.
The researchers sequenced antibody genes from 26 children, before and 40-50 days after their measles infection, and found that specific immune memory cells, which had been built up against other diseases and were present before the measles virus infection, had disappeared from the children’s blood. This would leave them vulnerable against infectious diseases they had previously been immune to.
This ‘immunological amnesia’ was tested directly in ferrets, which showed that infection with a measles-like virus reduced the level of their flu antibodies. The ferrets also had worse flu symptoms when infected with flu virus after the measles-like infection.
Author Professor Paul Kellam, from Imperial College London, said: “We showed that measles-like viruses can delete pre-existing flu immune memory from ferrets. Even after the ferrets had been successfully vaccinated against flu, the measles-like virus reduced levels of flu antibodies resulting in the animals becoming susceptible to flu infection again and experiencing more severe flu-like symptoms. This shows that measles could reverse the effects of vaccination against other infectious diseases.”
Professor Colin Russell, senior author from the University of Amsterdam, warned that the effect in some children was akin to being given powerful immunosuppressive drugs.
“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,” he added.
Dr Charlie Weller, head of vaccines at Wellcome, said: “These findings further strengthen the vital role the MMR vaccine plays in public health and protecting us from deadly disease. It is yet another reminder of how important vaccines are as a vital resource in eliminating infectious disease.”
Petrova V et al. Incomplete genetic reconstitution of B cell pools contributes to prolonged immune suppression after measles. Science Immunology 31 October 2019; doi: 10.1126/sciimmunol.aay6125
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