MMR Vaccine Could Invigorate the Innate Immune System to Fight COVID-19
As companies scramble to develop a vaccine against the SARS-CoV-2 virus, a team of husband and wife researchers have found that the measles, mumps, rubella (MMR) vaccine can reduce the symptoms of COVID-19. The finding doesn’t eliminate the need for a specific COVID-19 vaccine, but offers at least some protection for healthcare workers and other individuals who are at high risk of contracting COVID-19.
Reporting in the American Society for Microbiology (ASM), Paul Fidel Jr., Ph.D, associate dean of research at Louisiana State University Health School of Dentistry, and his wife, Mari Noverr, Ph.D., professor of microbiology & immunology at Tulane University School of Medicine, found that vaccination against MMR by immunocompetent individuals is not only safe, but also may be effective against the SARS-CoV-2 virus.
More specifically, Noverr’s lab, in collaboration with Fidel, found that vaccination with a live attenuated fungal strain of the MMR vaccine generated a response from the innate immune system against lethal polymicrobial sepsis. That protection was mediated by long-lived myeloid-derived suppressor cells (MDSCs) that in multiple experimental models had inhibited septic inflammation and prevented death. Therefore, the researchers suggest that an MMR inoculation also should induce MDSCs and thus inhibit or at least reduce the severe lung inflammation or sepsis associated with the progression of COVID-19.
The ability of live attenuated vaccines to train the immune system against non-targeted pathogen by training the host system against a variety of infections is a key feature of this approach. Evidence of its efficacy is growing.
Traditional vaccines seek to activate the adaptive immune system by causing the T- and B-lymphocytes to recognize specific pathogen. Then when a similar pathogen is encountered later, the adaptive immune system will remember that pathogen and launch a defense.
The innate immune system works differently. It recognizes pathogen through a system of pattern recognition receptors that quickly activate the host defense. The innate immune system does not, however, possess immunologic memory. During the past several years, clinical trials have shown that the innate immune cells – monocytes, macrophages and NK cells, for example – can confer protection from certain infections independently of the lymphocytes. Notably, this system provides nonspecific protection against infections unrelated to the target pathogen of the particular vaccine.
The milder symptoms seen in the 955 sailors on the USS Roosevelt who tested positive for COVID-19 (with only one hospitalization), are a real-world illustration of this effect.
MMR vaccinations are given to all U.S. Navy recruits, the researchers pointed out. Additional data noted a correlation between people in geographical locations who routinely receive the MMR vaccine and reduced COVID-19 death rates.
Research shows that countries with recent vaccination campaigns against measles-rubella have fewer COVID-19 deaths. There is a further correlation between those born after about 1971, when MMR vaccination became widespread, and low incidence of COVID-19. Hong Kong, for example, has 1,128 cases as of June 19, and 1.074 who had recovered from COVID-19. Only four people died. That’s a fatality rate of 0.4% in a population of 7.5 million.
The reason for such a low incidence rate may be the free MMR vaccination program instituted in 2019, for all adult healthcare workers, airport staff and foreign domestic helpers, and the 1997 mass immunization campaign for people from infancy to age 19.
Recentness of vaccination, therefore, also may play a role in the MMR vaccine’s protective abilities. Noting that COVID-19 rarely affects children, Fidel and Noverr hypothesize that youngsters’ more recent and frequent exposures to live attenuated vaccines induced the trained suppressive MCSCs and thus limited inflammation and sepsis associated with the viral infection.
Fidel and Noverr are proposing a clinical trial to determine the benefits of MMR vaccines as a protection against COVID-19, while specific vaccines are being developed for the disease.
"If adults got the MMR vaccination as children, they likely still have some level of antibodies against measles, mumps, and rubella, but probably not the myeloid-derived suppressor cells," Fidel said. "While the MDSCs are long-lived, they are not life-long cells. So, a booster MMR would enhance the antibodies to measles, mumps, and rubella and reinitiate the MDSCs.”
He advises healthcare workers, individuals in nursing homes and others at high risk of contracting COVID-19 to be vaccinated against MMR, in the hope that the innate immune response will be sufficient protection through the critical time of the pandemic, until CPVOD-19 vaccines are available.
“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," Fidel said.
Noverr recently was awarded a "Fast Grant" from the Emergent Ventures program at George Mason University to test the efficacy of MMR directly in a nonhuman primate model of COVID-19 infection.