MMR vaccine gives new hope against Covid-19

Administering the MMR (measles, mumps, rubella) vaccine could serve as a preventive measure to dampen septic inflammation associated with Covid-19 infection, says a team of experts from the US.

In an article just published in mBio, a journal of the American Society for Microbiology, immunology experts and microbiologists from Louisiana State and Tulane universities argue that administering the vaccine to high-risk adults such as health-care workers may have an added advantage and save lives.

“Live attenuated vaccines seemingly have some non-specific benefits as well as immunity to the target pathogen. A clinical trial with MMR in high-risk populations may provide a low-risk-high-reward preventive measure in saving lives during the Covid-19 pandemic,” said Dr Paul Fidel, associate dean for research and department chair of oral and craniofacial biology at Louisiana State University. “While we are conducting the clinical trials, I don't think it's going to hurt anybody to have an MMR vaccine that would protect against measles, mumps and rubella with this potential added benefit of helping against Covid-19.”

Fidel and colleagues argue that mounting evidence demonstrates that live attenuated vaccines provide non-specific protection against lethal infections unrelated to the target pathogen of the vaccine by inducing trained non-specific innate immune cells for improved host responses against subsequent infections. Live attenuated vaccines induce non-specific effects representing “trained innate immunity” by training immune system cells in the bone marrow to function more effectively against broader infectious insults.

In SA the triple vaccine against measles, mumps and German measles or rubella is often used in the private sector on infants aged nine months and again at 15 months. Only the measles vaccine is mandatory for all patients in SA.

But locally there seem to be different views among experts about the use of MMR on adults. Prof Mark Cotton, head of paediatrics and the infectious diseases unit at Stellenbosch University and Tygerberg Hospital, described the latest hypothesis as “interesting” and similar to that of the BCG vaccine. While MMR was currently used only on children in SA, Cotton said “vulnerable adults need it too”.

Scientists in New York recently compared countries with and without universal BCG policies, and found that countries that give the vaccine have lower Covid-19 infection rates.

“It is an interesting idea which could be tested. Repeating either measles or MMR vaccines is a good general public health measure as it will increase herd immunity. In the 2017 outbreak most measles was in the 20-44 year age group.

“The scientists have an interesting hypothesis that a live virus vaccine would stimulate the body’s immune system, similar to BCG ,” said Cotton.

Heather Zar,  head of child health at the University of Cape Town, said the suggestion that MMR inoculation could have a protective effect against Covid-19 should be viewed with caution as, it is only a hypothesis.

“There is no firm evidence to support the claim that MMR may help to protect against Covid-19. Currently this is being tested in animal models, and there are no human studies yet,” she said.

While it is possible that vaccines such as MMR and BCG induced immunity that is protective against other germs and not only limited to those they were developed against, Zar said more evidence is needed. She said there is also a hypothesis that suggests prior infection with seasonal coronavirus strains that circulate and cause mild infections in children, may too protect against Covid-19.

“But we need more studies and evidence before any recommendation can be made. I really don’t think we can recommend MMR for adults until there is much more evidence,” she said.

The US scientists said vaccination was conducted in a lab with a live attenuated fungal strain-induced trained innate protection against lethal polymicrobial sepsis. The protection was mediated by long-lived myeloid-derived suppressor cells previously reported inhibiting septic inflammation and mortality in several experimental models.

The researchers say that an MMR vaccine should be able to induce these cells that can inhibit or reduce the severe lung inflammation and sepsis associated with Covid-19 mortality.

The US researchers are proposing a clinical trial to test whether the MMR vaccine can protect against Covid-19, but in the meantime they suggest that all adults, especially health care workers and individuals in nursing homes, get the MMR vaccine. “If adults got the MMR as a child they likely still have some level of antibodies against measles, mumps, and rubella, but probably not the myeloid-derived suppressor cells. So, a booster MMR would enhance the antibodies to measles, mumps, and rubella and reinitiate the myeloid-derived suppressor cells,” said Fidel.