Here’s another reason to get a measles shot: Measles vaccination not only protects against measles, but reduces childhood deaths from other infections as well, a new study has found.
Researchers examined data on post-measles infections in the United States, England and Wales, and Denmark both before and after the measles vaccine became available in the 1960s. They found a correlation between the number of measles cases in a given period and the number of deaths from non-measles infectious diseases in children in the two to three years afterward.
“With mathematical analysis of all of the epidemiological evidence we have,” said the lead author, Michael J. Mina, who was a postdoctoral researcher at Princeton when the study was done, “it seems that when measles was prevalent, it would go through a population, and that population would be at increased risk for mortality from other diseases for about 28 months, and in proportion to how many people were infected with measles.” The findings were published in Friday’s issue of Science.
That measles depresses the immune response has been known for some time. Animal studies suggest that measles infection depletes B and T lymphocytes, specialized white blood cells that produce antibodies that “remember” the measles virus, providing immunity against further attacks.
The immune system then recovers, but for many months after, the cells that repopulate the system are almost all effective only against the measles virus. You will never get measles again, but you are temporarily left susceptible to other diseases.
“The immune system is working fine,” Dr. Mina explained. “But the assortment of stuff it protects against is decreased. Kids have to get re-exposed to other diseases to gain immunity to them.”
The measles vaccine provides immunity, too, but in a way different from measles infection. The attenuated live vaccine does not reduce the number of B and T lymphocytes, so their ability to fight other diseases is preserved.
The researchers calculate that when measles was common, it was a contributor to as many as half of all childhood deaths from infectious disease in industrialized countries.
Dr. Mina, now a medical student at Emory University, said that the measles vaccine has provided a significant added benefit in addition to protecting against measles. After the vaccine came into use, rates of both measles and non-measles infections dropped. The reduction in measles cases after the vaccine was introduced is the main reason for the reduction in rates of other infectious diseases.
“It’s the absence of measles that is driving down mortality from other diseases,” he said.
In industrialized countries, it is mainly deaths from respiratory infections that are prevented by the vaccine; in poor countries, the vaccine primarily reduces deaths from diarrheal diseases and dysentery. The effect has been significant, driving childhood infectious disease deaths in Western countries down to six per 100,000 after the vaccine from 16 per 100,000 before.
“This demonstrates at a new level why measles is not a benign infection. It puts children at risk for years,” Dr. Mina said. “More than anything else, it demonstrates the importance of getting rid of measles through vaccinations.”
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