It is widely known that the immunosuppression that follows measles leaves children vulnerable to opportunistic infections for weeks or even months. A recent study, however, shows that the negative effect on host resistance may extend up to 3 years. The suppressive effect has been attributed to “immune amnesia,” a byproduct of B and T lymphocyte depletion during the course of measles infection. During this period of immune memory cell loss, children are left vulnerable to the host of other dangerous and potentially fatal infectious diseases.
Research on vaccine use in poor countries has found that in the period following measles vaccination, both the rate of, and death from, other infectious diseases is lower than in the prevaccine era. The mechanism underlying this observation has been elusive. Results of a new study published in the journal Science report the same effect of measles vaccination in resource-rich countries and report for the first time the extended period of vulnerability.
An international team of researchers led by Michael Mina, a medical student at Emory University who led the study while at Princeton University, examined available data on measles cases and death rates from other infectious diseases before and after introduction of measles vaccination in the United States, England, Wales, and Denmark. In all locations measles cases declined as did death from non-measles infections. Deaths attributed to respiratory or diarrheal diseases in the US, for example, dropped from 18 per 100,000 pre-widespread vaccination to 6 per 100,000 after vaccination. The effect appeared to last for 2 to 3 three years after measles vaccination which suggests the interval required for the immune system to repair itself. The effect seems to be unique to the measles vaccine; analysis of pertussis data found no evidence that it causes similar immune amnesia.
The authors conclude: “Our data provide an explanation for the long-term benefits of measles vaccination in preventing all-cause infectious disease. By preventing measles-associated immune memory loss, vaccination protects polymicrobial herd immunity.”
Take-aways from the study compound the urgency to promote childhood vaccination:
♦ After a case of measles, children remain vulnerable to potentially fatal nonemeasles infectious diseases for as long as 3 years
♦ The time for immune system repair after infection with measles is much longer than originally believed – up to 3 years
♦ Vaccination against measles prevents the infection and, via preservation of the immune response, protects against other vaccine-preventable diseases
Mina MJ, Metcalf CJE, de Swart RL, Osterhause ADME, Grenfell BT. Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality. Science. 2015;348:694-699. DOI:10.1126/science.aaa3662 http://www.sciencemag.org/content/348/6235/694.short