On Aug. 17, 2021, researchers reported the delta variant of the virus that causes COVID-19 was not particularly good at evading the antibodies generated by vaccination, according to a study at Washington University School of Medicine in St. Louis.

The researchers analyzed a panel of antibodies generated by people in response to the Pfizer 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 Aug. 16 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, associate professor of pathology and immunology, of medicine and of 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.

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.