Why has measles vaccination on a large scale led to such a huge drop in childhood deaths, including many from diseases unrelated to measles?

Scientists have puzzled over that question for more than 50 years. Some speculated that measles deceives the immune system into forgetting how to battle other infections it's encountered in the past, a phenomenon known as immune amnesia. A new study published in the journal Science suggests the hunch was probably correct — and gives parents even more good reasons to vaccinate their kids.

Related: Don’t Let Measles Be your Travel Souvenir

Before this study, some researchers thought better hygiene or improved medical treatments might be responsible for the drop in childhood deaths from infectious diseases other than measles. Princeton University evolutionary biologist Michael Mina, PhD, and his colleagues used an elegantly simple mathematical model to investigate. They looked at fatalities from non-measles infections before and after the measles vaccine was introduced to four developed countries: the United States, England, Denmark and Wales.

Their finding? The drop in measles infections corresponded with a reduction in deaths from other diseases for up to three years after measles vaccination. (The average time was 27 months.) 

But was this simply part of a global trend toward fewer childhood deaths? The study refuted that. Although measles vaccinations were introduced to the U.S. and U.K. in the 1960s, they were not performed in Denmark until the 1980s. Despite being introduced 20 years later, the measles vaccine in Denmark was linked to the same drop in childhood deaths as the other three countries.

The researchers concluded the measles virus causes the body to “forget” part of the immunity it had painstakingly developed against other diseases. This means that while you're recovering from the measles — and for up to three years afterward — it's easy for infections like pneumonia to take hold.

“Our results show that when measles was common, measles virus infections could have been implicated in as many as half of all childhood deaths from infectious disease,” the authors wrote.

Measles may be special in its ability to induce immune amnesia. Researchers looked at whooping cough (pertussis) vaccinations to see whether they were linked to a drop in deaths from other diseases, but found they were not.

Quelling outbreaks 

Despite the life-saving benefits of the measles vaccine, measles outbreaks in the United States have been on the rise. After reaching a record low in 2004, when only 37 cases have been reported, by 2014 the number of confirmed cases had climbed to 648.

Related: Measles Outbreak Linked to Unvaccinated Woman Who Visited Disneyland

Some outbreaks have been traced to unvaccinated travelers bringing measles to the United States. The measles comeback is also associated with a growing number of parents, often from high-income communities, who have refused to get their children the measles-mumps-rubella vaccination (MMR) due to fears of complications.

Some parents worry the MMR vaccination might trigger childhood autism a theory advanced by a 1998 study that turned out to be fraudulent and was later retracted. Numerous other studies have discredited the link between the measles vaccine and autism, most recently a large study published in Journal of the American Medical Association. The JAMA study found the MMR shot doesn’t raise the risk of autism, even among children who are at increased genetic risk of developing the condition.

Related: Another Study Finds No Vaccine-Autism Link

The risks from getting measles are far higher than the risks from a vaccination, experts say. Measles complications include such life-threatening diseases as pneumonia and encephalitis, a brain inflammation that in rare cases can lead to coma and death.

The study in Science suggests the risks of contracting these potentially deadly illnesses can last up to three years after getting measles but that getting the vaccination slashes this risk.

Measles vaccination protects “herd immunity,” Mina and his team concluded. That means the vaccine protects our population, or “herd,” by cutting the number of measles cases to the point where even people who can't be vaccinated for one reason or another probably won't contract the disease. 

This is yet another reason to get your kids vaccinated — and yourself if you were born later than 1956 and never got the MMR or never had the three diseases it protects against, including measles. 

Diana is an award-winning writer and editor with more than 20 years' experience in magazine, video, book and digital journalism, with a specialty in health coverage. She was a longtime writer and news editor at the Center for Investigative Reporting; has written for publications from the Washington Post to the Times of London syndicate; and has served as a senior and/or consulting editor at Time Inc. Health, Hippocrates, HealthDay News Service and Reporting on Health. She was also editor in chief of Consumer Health Interactive, a national health and medical web site, and has reported on finance for Blueshift Research and PBS Frontline. Before joining SafeBee, she was editor of Bioenergy Connection, a national magazine about bioenergy at UC Berkeley. Her favorite safety tip: Wear a bike helmet.