SARS-CoV-2 Delta variant struggles to evade some antibodies

Aug. 20, 2021

Despite causing a surge in infections this summer that has resulted in thousands of hospitalizations and deaths, the Delta variant of the virus that causes COVID-19 is not particularly good at evading the antibodies generated by vaccination, according to a study by researchers at Washington University School of Medicine in St. Louis, which was summarized in a news release.

The researchers analyzed a panel of antibodies generated by people in response to the Pfizer-BioNTech COVID-19 vaccine and found that Delta was unable to evade all but one of the antibodies they tested. Other variants of concern, such as Beta, avoided recognition and neutralization by several of the antibodies.

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

In previous studies, co-senior author Ali Ellebedy, PhD, Associate Professor of Pathology & Immunology, Medicine and Molecular Microbiology, had shown that both natural infection and vaccination elicit lasting antibody production. But the length of the antibody response is only one aspect of protection. The breadth matters, too. An ideal antibody response includes a diverse set of antibodies with the flexibility to recognize many slightly different variants of the virus. Breadth confers resilience. Even if a few antibodies lose the ability to recognize a new variant, other antibodies in the arsenal should remain capable of neutralizing it.

To assess the breadth of the antibody response to SARS-CoV-2, the researchers extracted antibody-producing cells from three people who had received the Pfizer-BioNTech 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 recognized alpha and delta, eight recognized all four variants, and one failed to recognize any of the four variants.

Scientists gauge an antibody’s usefulness by its ability to block virus from infecting and killing cells in a dish. So-called neutralizing antibodies that prevent infection are thought to be more powerful than antibodies that recognize the virus but can’t block infection, although both neutralizing and non-neutralizing antibodies contribute to defending the body.

The researchers found that five of the 13 antibodies neutralized the original strain. When they tested the neutralizing antibodies against the new variants, all five antibodies neutralized delta, three neutralized alpha and delta, and only one neutralized all four variants.

The antibody that neutralized 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.

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