Doctors at Washington University are investigating whether the commonly used measles, mumps and rubella vaccine could protect people against getting sick with the coronavirus.

The large international study is based on the concept of trained immunity — the idea that live vaccines can turbocharge the immune system.

“Of course it protects people from measles mumps and rubella, but activating the immune system with this type of vaccine could stimulate protection from other viruses as well,” said Dr. Mary Politi, a professor at Washington University and one of the researchers in the study. “The structural similarities might mean (that) when the body produces this response with antibodies with MMR, they could recognize the virus that causes COVID-19.”

The MMR vaccine could also trigger a more general immune response that could protect against multiple viruses, including the coronavirus, she said.

Washington University is coordinating the study in collaboration with other schools in England and South Africa. Researchers will give either a vaccine or a placebo to 30,000 health care workers in at least nine countries. Then they’ll see if those who received the vaccine have protection from the coronavirus or less severe symptoms if they do get sick.

Unlike the common flu shot, the MMR vaccine is what is called a “live” or “attenuated” vaccine. That means it contains a weakened form of the virus it protects against.

That’s key to its potential success, said Dr. Michael Avidan, another Wash U professor and principal investigator in the study.

“What seems to happen is when you get one of these live attenuated vaccines, it trains your immune system, and this lasts for a couple of months to a few years,” he said. “So [if] a year later you’re exposed to another infectious agent, your immune system is primed and ready in a robust and brisk way to fight off this new infection.”

“Trained immunity” only lasts for a short time, Avidan said. That’s why those who have received the MMR vaccine in the past may not be protected from COVID-19.

There’s also evidence live immunizations could protect against other viruses, Politi said. Earlier this year, close to 1,000 Marines, who receive MMR vaccinations when they join the military, were exposed to the coronavirus on a ship. Though many became sick, only one needed to be hospitalized.

It also could be why children, who may have received immunizations more recently, may not get as sick with the coronavirus as adults, Politi said.

If the study proves the MMR vaccine is effective, it could help protect people until a coronavirus vaccine or treatment is developed.

The vaccine has been proven safe, and there’s a huge supply of it worldwide, Avidan said.

“If it works, we could easily deploy it across the whole world,” he said. “We could use it for this pandemic and other pandemics.”

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