The Measles-Mumps-Rubella (MMR) and Tetanus-Diphtheria-Pertussis (Tdap) vaccines have been associated with increased protection against COVID-19 and reduction in severity of the disease, according to a study. The researchers at Brigham and Women’s Hospital in the US noted that vaccines are designed to induce a strong and long-lasting immune response through the creation of memory T cells and B cells.
The MMR vaccine, given during early childhood, and Tdap preventive, given every 10 years, are known to elicit a protective response against the diseases from which the vaccines get their names, they said.
However, it is possible that these vaccines may also elicit cross-reactive memory T cells capable of responding to protein targets called antigens present in other disease causing microbes, including the viral antigens in SARS-CoV-2.
The study, published in the journal Med, suggests 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 the virus, thereby lowering the risk of severe disease.
The researchers conducted laboratory-based analyses using sensitive, new techniques to detect and characterise T cell responses to antigens.
They applied these techniques to measure the response of T cells isolated from the blood of COVID-19 convalescent patients and patients vaccinated against the disease to antigens from SARS-CoV-2 and the MMR and Tdap vaccines.
The team, including researchers from Cleveland Clinic, US, leveraged a large, well-annotated cohort of COVID-19 patients and found that prior MMR or Tdap vaccination was associated with decreased disease severity.
The researchers “observed 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,” said study co-author Andrew Lichtman from the Brigham and Women’s Hospital.
“Although previous smaller studies suggested a similar link, our in-depth epidemiological analyses, together with our basic research results, suggest that these commonly given vaccines may protect against severe disease,” Lichtman said.
The researchers noted in laboratory experiments using COVID-19 convalescent blood that whenever they observed a heightened T cell response to SARS-CoV-2 proteins, they also saw an increased 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, they said.
The researchers also performed a retrospective cohort study using data from more than 75,000 patients in Ohio or Florida who had tested positive for COVID-19 between March 8, 2020, and March 31, 2021.
They found that patients who had previously been vaccinated for MMR had a 38 per cent decrease in hospitalisation and a 32 per cent decrease in ICU admission or death.
Similarly, patients previously vaccinated for Tdap had 23 per cent and 20 per cent decreased rates, respectively, of these outcomes, according to the study.
“Beyond learning about the potential benefits of the MMR and Tdap vaccines in the context of COVID-19, this study provides a blueprint for accelerating research,” said study co-author Lara Jehi, Chief Research Information Officer of the Cleveland Clinic Health System.
The researchers noted that while their laboratory-based findings are strengthened by the epidemiological observations, further work is needed to assess the association between the MMR and Tdap vaccinations and severity of COVID-19 disease to determine if the relationship is a causal one.
Prospective studies of vaccination and patient outcomes may help distinguish correlation from causation, they added.