Vaccinations and prior infections with earlier COVID-19 virus variants strongly boost T-cell immunity against the omicron variant, according to a just-released preprint study by a team of researchers led by South African virologists Wendy Burger and Catherine Riou. The omicron variant often evades our bodies' first line of defense against infections: the antibodies induced by infections from earlier COVID-19 variants and vaccines that aimed at those same variants. While fast-reacting antibodies can prevent infections entirely, the number of antibodies produced in response to vaccinations and infections fall over time. That's where our bodies' second line of immunological defense—called T cells—comes into play.
Created by vaccinations and infections, T cells lurk in our bodies waiting to be activated when they are invaded by disease microbes. Some T cells directly attack and kill cells that have been infected, as these infected cells reproduce the virus; other T cells help B cells to rev up the production of additional antibodies to defend against the infection.
The South African researchers wanted to know how well T cells, which they collected from the blood samples of 50 patients who had been vaccinated or infected by earlier COVID-19 variants, would react to the omicron variant. Their concern was that the highly mutated omicron variant would not be recognized by the T cells that resulted from vaccinations against or infections from earlier COVID-19 variants. Happily, they report that this is not the case.
"Despite extensive neutralization escape against Omicron, 70-80% of the T cell response is preserved," they report. Neutralization escape means that waning antibodies are not enough to prevent infections by the omicron variant in a significant proportion of those vaccinated or previously infected by earlier variants. Nevertheless, T-cells remain 70-80 percent effective at defending against omicron infections.
Consequently, the researchers conclude: