How Pfizer COVID vaccine cuts risk of Delta infection

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New York: Despite causing a surge in infections that has resulted in thousands of hospitalisations and deaths, the Delta variant of COVID-19 is not particularly good at evading the antibodies generated by the Pfizer vaccine, according to a study.

The findings, published in the journal Immunity, help explain why vaccinated people have largely escaped the worst of the delta surge.

Researchers at Washington University in the US extracted antibody-producing cells from three people who had received the Pfizer vaccine. They grew the cells in the laboratory and obtained from them a set of 13 antibodies that target the original strain that began circulating last year.

The researchers tested the antibodies against four variants of concern: alpha, beta, gamma and delta. Twelve of the 13 recognised alpha and delta, eight recognised all four variants, and one failed to recognise any of the four variants.

Five of the 13 antibodies neutralised the original strain. When the team tested the neutralising antibodies against the new variants, all five antibodies neutralised delta, three neutralised alpha and delta, and only one neutralised all four variants.

"The fact that delta has outcompeted other variants does not mean that it's more resistant to our antibodies compared to other variants," said Jacco Boon, Associate Professor of medicine, of molecular microbiology and of pathology and immunology at the University's School of Medicine in St. Louis.

The antibody that neutralised all four variants of concern -- as well as three additional variants tested separately -- was called 2C08. In animal experiments, 2C08 also protected hamsters from disease caused by every variant tested: the original variant, delta and a mimic of beta.

Some people may have antibodies just as powerful as 2C08 protecting them against SARS-CoV-2 and its many variants, said Ali Ellebedy, Associate Professor of pathology and immunology, of medicine and of molecular microbiology, at the varsity.

Using publicly available databases, the researchers discovered that about 20 percent of people infected or vaccinated against SARS-CoV-2 create antibodies that recognise the same spot on the virus that is targeted by 2C08. Moreover, very few virus variants (.008 percent) carry mutations that allow them to escape antibodies targeting that spot.

"The ability of a variant to spread is the sum of many factors. Resistance to antibodies is just one factor. Another one is how well the variant replicates. A variant that replicates better is likely to spread faster, independent of its ability to evade our immune response. So delta is surging, yes, but there's no evidence that it is better at overcoming vaccine-induced immunity compared to other variants," Boon said.