While Delta is still the most common variant in all continents except Africa, Omicron is spreading very quickly. Fully vaccinated people with no travel history have also tested positive for Omicron, raising doubts over effectiveness of the existing Covid-19 vaccines, discussions on the need for a booster dose, and speculations of a third wave.
As Omicron is said to have mutations that may be helping it escape the body’s first line of defence, antibodies, studies have highlighted a bigger role that the immune system’s second line of defence, T-cells, may play. T cells, the body’s weapon against virus-infected cells, were primed enough by vaccination that they defended against Omicron, separate studies have found.
What are T-cells?
T-cells are white blood cells that can remember past diseases, attack virus-infected cells or help in production of antibodies to counter them. Unlike antibodies, T-cells can target the whole of the virus’s spike protein, which remains largely similar even in the highly mutated omicron.
T cells are highly effective at recognising and attacking the Omicron variant, thereby preventing most infections from progressing to critical illness, a study has showed.
The ‘T’ stands for thymus, the organ in which the cells’ final stage of development occurs.
A study from the University of Cape Town’s Institute of Infectious Disease and Molecular Medicine, which looked at patients, who had recovered from Covid or been vaccinated, found that 70% to 80% of the T-cell responses they assessed held up against Omicron.
“Despite Omicron’s extensive mutations and reduced susceptibility to neutralising antibodies, the majority of T-cell response, induced by vaccination or natural infection, cross-recognises the variant,” the researchers said.
In another study, researchers from Erasmus University in the Netherlands looked at 60 vaccinated healthcare workers and found that while their antibody responses to Omicron were lower or non-existent compared with the beta and delta variants, T-cell responses were largely unaltered, “potentially balancing the lack of neutralising antibodies in preventing or limiting severe Covid-19.”
In test tube experiments, researchers in South Africa exposed copies of the virus to T-cells from volunteers who had received vaccines from Johnson & Johnson or Pfizer/BioNTech or who had not been vaccinated, but had developed their own T-cells after infection with an earlier version of the coronavirus.
“Despite Omicron’s extensive mutations and reduced susceptibility to neutralizing antibodies, the majority of T-cell response, induced by vaccination or natural infection, cross-recognizes the variant,” researchers say.
“Well-preserved T-cell immunity to Omicron is likely to contribute to protection from severe Covid-19,” which supports what South African doctors had initially suspected when most patients with Omicron infections did not become seriously ill, they said.