Children who survive a measles infection may live with a weakened immune system for up to three years, leaving them highly susceptible to a host of other deadly diseases, scientists have warned.
The measles virus can cause serious disease in children by temporarily suppressing their immune systems. This vulnerability was previously thought to last a month or two.
The new study provides epidemiologic evidence that measles may throw the body into a much longer-term state of "immune amnesia," where essential memory cells that protect the body against infectious diseases are partially wiped out.
"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 University.
"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," Metcalf said.
"Our findings suggest that measles vaccines have benefits that extend beyond just protecting against measles itself," said lead author Michael Mina, a student at Emory University School of Medicine who worked on the study as a postdoctoral researcher at Princeton.
The researchers looked at deaths among children between the ages of 1 and 9 in Europe, and 1 and 14 in the US, in both pre- and post-vaccine eras.
They ran a basic association test, comparing measles incidence and deaths. The initial analysis came back statistically significant but weaker than expected, not showing a strong connection between the two.
At this point, Mina and his collaborators decided to evaluate the data making different assumptions about how long the possible immune-amnesia effects of measles may last.
This exploration uncovered a very strong correlation between measles incidence and deaths from other diseases, allowing for a "lag period" averaging roughly 28 months after infection with measles.
This finding was consistent in all age groups across the three countries and also consistent in pre- and post-vaccine eras.
"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," Grenfell said.
The research findings suggest that - apart from the major direct benefits - measles vaccination may also provide indirect immunological protection against other infectious diseases.
