The measles virus is known to temporarily suppress children's immunes systems, but new research suggests these effects could last for as much as three years.
The study provides the first epidemiologic evidence that measles can throw the body into a long-term state of "immune amnesia," in which memory cells that fight diseases are partially wiped out, Princeton University reported.
"We already knew that measles attacks immune memory, and that it was immunosuppressive for a short amount of time. But this paper suggests that immune suppression lasts much longer than previously suspected," said C. Jessica Metcalf, co-author and assistant professor of ecology and evolutionary biology and public affairs at Princeton. "In other words, if you get measles, three years down the road, you could die from something that you would not die from had you not been infected with measles."
The findings suggest the measles vaccine could have even more benefits than we thought it did, and that it can protect against more diseases than only the measles themselves.
"It is one of the most cost-effective interventions for global health," said lead author Michael Mina, a student at Emory University School of Medicine who worked on the study as a postdoctoral researcher at Princeton.
Past research has shown that when the measles virus attacks T lymphocytes (which causes immune memory against other diseases), it creates immune amnesia. After a period of about a month, the immunes cells are replenished, but solely focus on the measles and ignore other invading infections. Mina analyzed how quickly the immune system switches back to "broad protection" by looking at data available from the U.S., England and Wales, and Denmark. They examined deaths among children between the ages of 1 and 9 in Europe and 1 and 14 in the U.S. from both pre and post vaccination eras. A basic association test comparing measles incidence and death came back with statistically significant results showing a connection between the two, but it was relatively weak.
The team chanced the assumption about how long the possible immune-amnesia effects of the virus lasted, and found a much stronger positive correlation between measles cases and deaths from other diseases.
"In other words, reducing measles incidence appears to cause a drop in deaths from other infectious diseases due to indirect effects of measles infection on the human immune system," said Bryan Grenfell, the Kathryn Briger and Sarah Fenton Professor of Ecology and Evolutionary Biology and Public Affairs at Princeton. "At the population level, the data suggests that when measles was rampant, it may have led to a reduction in herd immunity against other infectious diseases."
The findings were published in a recent edition of the journal Science.
