The Measles-Mumps-Rubella (MMR) vaccine, given during early childhood, and Tetanus-Diphtheria-Pertussis (Tdap) vaccine, given every 10 years, may help lower the risk of severe Covid-19, according to researchers.
Besides eliciting a protective response against the diseases it is possible that both MMR and Tdap vaccines may also elicit cross-reactive memory T cells capable of responding to protein targets called antigens that are present in other microbes that cause diseases -- including the viral antigens in SARS-CoV-2, said researchers from the Brigham and Women's Hospital in the US.
Using data from more than 75,000 patients who had tested positive for Covid-19 between March 8, 2020, and March 31, 2021, the team found that patients who had previously been vaccinated for MMR had a 38 per cent decrease in hospitalisation and a 32 percent decrease in ICU admission/death. Similarly, patients previously vaccinated for Tdap had 23 per cent and 20 per cent decreased rates, respectively, of these outcomes.
The concept is that pre-existing memory T cells generated by prior MMR or Tdap vaccination and activated by SARS-CoV-2 infection give the immune system a head start in responding to SARS-CoV-2, thereby lowering the risk of severe Covid-19, the researchers explained.
Their results, published in the journal Med, found "an association where individuals with Covid-19 who had either MMR or Tdap vaccines had a much lower frequency of going to the intensive care unit or dying". The study also emphasised the importance of routine vaccination for children and adults, which have been affected in many countries due to Covid.
In a separate laboratory experiment using Covid-19 convalescent blood, whenever the team observed a heightened T cell response to SARS-CoV-2 proteins, they also saw a heightened response to proteins from MMR and Tdap, which they had been using as controls. This was observed with both Covid-19 convalescent and uninfected individuals vaccinated against SARS-CoV-2.
"Although MMR and Tdap are not a substitute for Covid-19 vaccines they may afford greater and more durable protection, possibly against emerging spike variants than the Covid-19 vaccine alone," said Tanya Mayadas, a senior scientist in the Brigham's Department of Pathology and Professor of Pathology at Harvard Medical School.
"And in areas where the Covid-19 vaccines are not available, they could protect infected individuals from developing severe disease," she added.