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Measles vaccine — in addition to preventing measles — is known to provide additional benefit: In the period following vaccine receipt, the rate of all infectious diseases is lower than it was in the prevaccine era. This effect has been described primarily in resource-poor countries, and the underlying mechanism has remained unexplained.
Now, researchers show that the additional nonspecific benefit from measles vaccine is likely due to avoidance of the immunosuppressive effects of measles disease. (Depletion of T and B lymphocytes following measles infection is believed to cause these effects.) They also show that the benefit lasts longer than was previously recognized.
The researchers examined available data on vaccination rates and nonmeasles infectious disease deaths of children in the U.K., the U.S., and Denmark. In each of these locations, there was a drop in the nonmeasles mortality rate that paralleled the introduction of measles vaccine and the subsequent decrease in the rate of measles infection. This phenomenon appeared to last for 2 to 3 years and is likely unique to measles vaccine. Analysis of data on pertussis, another vaccine-preventable disease, showed no evidence that it causes immunosuppression.
Mina MJ et al. Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality. Science 2015 May 8; 348:694. (http://dx.doi.org/10.1126/science.aaa3662)
Comment
The unexpected dividend from measles vaccine — reduction of nonmeasles infections — appears to occur in high-income countries as well as in resource-poor ones and is likely explained by avoidance of measles-associated immune memory cell loss. This should be an additional reason to ensure that all of the world's children have access to the vaccine.