They’re proposing giving a booster dose of the measles, mumps and rubella (MMR) vaccine to people to see if it ramps up immunity in general, perhaps helping prevent some of the most severe effects of Covid-19.
Their thinking: The MMR vaccine is known to protect kids against infections that go far beyond the three viruses targeted by the vaccine. The theory is that the vaccine boosts general immunity, in addition to training the body to recognize specific viruses.
The MMR vaccine is what’s known as a live vaccine. It uses highly weakened, or attenuated, versions of the measles, mumps and rubella viruses to produce immune protection without making people sick. Because it uses whole viruses, it stimulates an immune response that is broad and goes beyond the production of antibodies.
“There is mounting evidence that live attenuated vaccines provide nonspeciﬁc protection against lethal infections unrelated to the target pathogen of the vaccine by inducing ‘trained’ nonspeciﬁc innate immune cells for improved host responses against subsequent infections,” Paul Fidel of Louisiana State University and Mairi Noverr of Tulane University wrote in a letter to the journal mBio.
“If we’re wrong, well, at least people will have new antibodies to measles, mumps and rubella. So there’s no harm, no foul,” Fidel told CNN.
“We emphasize this is strictly a preventive measure against the worst inﬂammatory sequelae of COVID-19 for those exposed/infected and does not represent an antiviral therapy or vaccine against COVID-19 in any manner,” Fidel and Noverr added in their letter.
One theory about why children and teens have much lower rates of coronavirus infection is that they have more recently received vaccines, including MMR, than adults have, and have some of the residual extra immune benefits. Some countries are giving people booster shots of a tuberculosis vaccine for this reason, and some experts have proposed using polio vaccines for a similar purpose.
Some vaccine experts are dubious about the theory that children are less vulnerable to coronavirus because of recent vaccinations.
Dr. Peter Hotez, a pediatrics professor at the Baylor College of Medicine, said children could be less vulnerable because they have more recently been infected with some of the other coronaviruses that cause the common cold.
“This might stimulate local or systemic cross protecting immunity,” Hotez told CNN.
Or there’s another possibility. “A more likely explanation is the lower expression of the ACE2 receptor in the upper respiratory tracts of children,” said Dr. Paul Offit of the Children’s Hospital of Philadelphia. The ACE2 receptor is a molecular doorway that is used by the new coronavirus to get into cells.