Children who survive an outbreak of measles may have to live with a weakened immune system for up to three years, leaving them more susceptible to other types of potentially deadly diseases, scientists have warned.
The measles virus can not only severely sicken children, but also weakens their immune systems. Scientists previously believed that this weakened state only lasted a month or two, but a new study provides epidemiologic evidence that the measles may cause the body to experience "immune amnesia" for much longer than originally thought. This amnesia is caused by the essential memory cells that protect the body against infectious diseases being partially wiped out by the measles virus.
"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 United States, in both pre- and post-vaccine eras. They ran an 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.
Researchers then decided to evaluate the data making different assumptions about how long the possible immune amnesia effects of measles may last. This research uncovered a very strong correlation between measles incidence and deaths from other diseases, with the period averaging about 28 months after the infection with measles.
The findings were consistent in all age groups across three countries and also consistent in both pre- and post-vaccine time periods.
"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.
These findings suggest that apart from the direct benefits of the measles vaccine, it may also provide an indirect immunological protection against other diseases as well.
