The Advantages of Vaccines

A new study shows that vaccination with a weakened strain of salmonella not only protects against typhoid fever but also seems to rev up the immune system to fight off other problems like influenza and yeast infection.

By chance, in an earlier study looking at how the typhoid oral vaccine affects the gut, researchers noticed that the vaccine also triggered a protective response against influenza. So they designed a new study of 16 adults, reported Feb. 27 in the journal Science Advances, to look specifically at the broader, indirect effects of the vaccine on other infections. “This was the first time anyone looked at typhoid vaccine in this way,” says Shaun Pennington of the Liverpool School of Tropical Medicine, who has a Ph.D. in infection and immunity and is an author of the new study.

But this small study “fits into a larger story,” says Dr. Michael Mina, a pathologist at the Harvard T.H. Chan School of Public Health who studies how measles and the measles vaccine influence the immune system. “Live vaccines have the very broad benefit of going much further than protecting just against the targeted disease.” Mina was not involved in the new typhoid study.

For decades, scientists have observed an extraordinarily positive side effect among children who received the measles vaccine: Deaths from measles plummeted among vaccinated children and so did deaths from unrelated diseases like pneumonia and diarrhea.

The same result has been found as a consequence of live polio vaccine and Bacille Calmette-Guerin, or BCG, vaccine for tuberculosis. When those vaccines are introduced to poor areas of the world, studies have shown, deaths from many other causes, not just the vaccine-targeted disease, go down.

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