In unvaccinated children, 'immune amnesia' occurs in the wake of measles infection

October 31, 2019

Two separate investigations into the immune systems of 77 unvaccinated children before and after measles infection have revealed the infection can cripple immunity against viruses and bacteria for the long-term, creating a kind of "immune amnesia" that leaves individuals more vulnerable to future infections by other pathogens. Based on these findings, published in Science Immunology and Science, scientists emphasize once more the need for widespread vaccination, which may not only prevent measles, but may also prevent the weakening of "herd immunity" to other kinds of pathogens.

Before the introduction of the measles vaccine, nearly every child experienced measles infection. Vaccination has helped lead to an 80% reduction in measles cases between 2000 and 2017, saving an estimated 21.1 million lives. However, because of a combination of antivaccination campaigns, nonvaccinating religious communities, and limited access to the vaccine, measles continues to affect more than seven million people annually worldwide, causing upwards of 100,000 deaths. Reduced vaccination alone has led to a nearly 300% increase in measles infections since 2018. To help estimate the impact of vaccination, Velislava Petrova et al. and Michael Mina et al. investigated the hypothesis that measles can instigate immune suppression, which can persist for months to years even after the disappearance of visible symptoms, like the characteristic measles rash. This hypothesis has already been supported by previous studies, including evidence that associates measles with up to 50% of childhood deaths from infectious diseases. However, precisely how post-measles immune suppression unfolds in humans is unknown. In Science Immunology, Petrova and colleagues sequenced antibodies produced by B cells - one of the primary immune cells able to recognize a virus and deploy attacks against it - from 77 unvaccinated children. The children ranged in age from four to 17 years old, did not have a history of natural measles and were from three Orthodox Protestant schools in the Netherlands. By comparing the children's B cell data before and after measles infection, the researchers identified two indications of immune suppression from measles: incomplete restocking of the B cell pool and compromised immune memory due to depletion of B cell clones. In additional animal studies, the scientists found measles-infected ferrets already vaccinated against the flu became less immune to the virus and experienced more severe symptoms upon secondary flu infection.

In Science, Mina and colleagues used a tool called VirScan to analyze the responses of antibodies in the unvaccinated children before and after measles infection. The technology tracks antibodies to thousands of viral and microbial antigens in the blood. The researchers found that the disease wiped out 11 to 73% of the antibody repertoire across individuals two months after measles infection, severely compromising immune memory of various infectious agents even after recovery. Antibody depletion was not observed in infants vaccinated against measles, mumps and rubella. Furthermore, in measles-infected macaques, 60% of the antibody repertoire was undetectable for at least five months. Though rebuilding the antibody repertoire is possible through reexposure to the pathogens, this could take months or years and might pose several health risks, the authors say. A related Focus by Duane Wesemann describes both studies in further detail.

American Association for the Advancement of Science

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