Microscope image of coronavirus showing spike protein. Credit: U.S. National Institutes of Health

A computational study shows that the current spike protein vaccines are effective against a number of SARS-CoV-2 variants1. Despite a drop in neutralising antibody responses, the vaccines probably induce immune responses by generating T cells, a type of white blood cells that kill viruses.

This analysis suggests T cells can fight the viruses and protect against COVID-19 after vaccination, says a team at the Indian Institute of Technology Madras in Chennai.

A multitude of factors other than neutralising antibodies determine vaccine efficacy. T-cell response is one factor yet to be studied extensively.

To better understand this, the scientists analysed the molecular differences in T-cell epitopes across a few variants – Delta plus, Gamma, Zeta, Mink and Omicron. Epitopes are the smallest unit of an antigen, a pathogenic particle to which a T cell or an antibody can bind.

The researchers, led by Vani Janakiraman, found that several epitopes undergone mutations. But 90% of the epitopes which were conserved in the all the variants except Omicron, could trigger T-cell responses.

This means that the changes to the epitopes are not large enough to evade the T-cell immune response that the body learned through vaccination. The conserved T cell responses may lead to vaccines retaining their potential to fight severe and fatal COVID-19 infections, the researchers note.