As the roll-out of the Covid vaccine booster shots slowly gathers pace across the country, a new study has strengthened evidence that people who received the third dose of an mRNA vaccine are much better protected from any severe illness that could be caused by the newly-emerging strains including Omicron.
The findings of the latest study published in the peer-reviewed scientific journal Nature shed light on how a booster dose of an mRNA vaccine which was in fact developed to fight the original circulating Covid-19 strain, increases the capacity of our immune system – to produce a broader range of virus-neutralising antibodies, including those which can neutralise the new omicron variant – compared to the standard two-doses.
The findings are particularly significant, as India too has recently opened the booster shot availability to all adults above 18 years this April, but the enthusiasm among people to get jabbed for the third time remains low. This could be a matter of concern in the wake of the sudden spike in infections across the country, which has recorded as many as 2,541 fresh cases in the last 24 hours, and 30 deaths.
According to the government, as many as 26.2 million individuals aged above 60 years, including healthcare workers, and 4.17 lakh among those aged between 18-60 years have so far been vaccinated for the third dose. Over 69,423 received the booster dose in the last 24 hours.
Rapid immune response, more potent & broader antibodies
Scientists from New York’s Rockefeller University analysed blood samples from 42 volunteers (23-78 years) in the US who received three doses of an mRNA vaccine. Eight received Moderna, and 34 of them got Pfizer-BioNTech, and the samples were collected after 2.5 weeks of the first dose, 1.3 and 5 months after the second dose and a month after the third dose. None of the participants in the study, which was conducted during Jan-December 2021 had previously been infected with the virus.
The researchers observed an increase in the range and potency of memory B cells – which can respond rapidly and produce antibodies that could neutralise the original Covid-19 virus- compared to those produced after a second dose.
Most significantly, more than 50% of these antibodies were shown to neutralise the Omicron variant, the team noted. This happened, despite the fact that these mRNA vaccines were developed to fight the original Covid-19 strain, and were not designed to specifically target the Omicron strain that carries as many as 35 mutations in its spike protein.
The researchers further explained that the increase in antibody potency after the third dose was because antibodies from the newly-emerging memory B cells targeted more regions of that part of the virus that facilitates its entry into the host cells, compared to the ones which were released after the second dose.
“Thus, individuals receiving three doses of an mRNA vaccine, have a diverse memory B cell repertoire that can respond rapidly and produce antibodies capable of clearing even diversified variants such as Omicron. This data helps in explaining why a third dose of a vaccine that was not specifically designed to protect against variants is effective against variant-induced serious disease,” the team noted.
Breakthrough infection concerns remain
Although a third dose boosts antibody responses against multiple Covid-19 variants, scientists maintain that it will not be able to prevent breakthrough infection in all cases.
“A rapid recall by memory T cells and a diversified and expanded memory B cell compartment are likely to be key mechanisms that contribute to the enhanced protection against severe disease by a third mRNA vaccine dose,” they concluded.
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