With vaccination rolling around the world, it might feel for some that life is getting back to normal. But concern around the Delta variant has been growing. It has now been detected in over 130 countries, including 65 in July and early August. Three other variants of concern, Alpha, Beta, and Gamma, are also circulating in the United States.
Recently, a study led by Shane Crotty from La Jolla Institute for Immunology published in Cell Reports Medicine found that T cells that develop as a defense mechanism in people who had recovered from COVID-19 or had received Moderna or Pfizer vaccines remain effective against the Alpha, Beta, and Gamma SARS-CoV-2 variants, along with another variant called CAL.20C. The Johnson & Johnson vaccine had not been available at the time Crotty was doing this research.
“You can think of T cells as a backup system: if the virus gets past the antibodies — if you have vaccine T cells the T cells can probably still stop the variant coronavirus infection before you get pneumonia," said Crotty in Science Daily.
While vaccine development has heavily focused on the antibody response of the body generated by B cells, new variants have mutations in the spike protein that can escape antibody recognition. In April, theoretical research by Binquan Luan and Tien Huynh showed that new mutations can sacrifice a tighter attachment to the human receptor ACE2 to gain antibody evasion abilities.
So far, studies have not converged on whether the Delta variant can cause more severe illness than the original strain in unvaccinated people. However, researchers have verified that two doses of an mRNA vaccine are effective at preventing hospitalization or death, which they report in a recent pre-print. More studies are required to understand vaccine breakthrough infections.
On July 27, WHO highlighted the urgent need to increase COVID-19 vaccination coverage and the recommendation for everyone to use the strategies that have been in place for the past year, including wearing masks in indoor public places.