Virology: Delta variant partially able to escape antibody neutralization

The Delta variant of SARS-CoV-2 is resistant to some of the laboratory-made monoclonal antibodies, and less inhibited by antibodies in the sera of individuals who were previously infected with SARS-CoV-2 or individuals who received one dose of either the Pfizer–BioNTech or AstraZeneca vaccine. The findings are published online in Nature this week. However, the paper reports that a neutralizing response is generated against the Delta variant after two doses of the respective vaccines.

Olivier Schwartz and colleagues investigated how reactive monoclonal antibodies and antibodies in blood sera from 103 individuals with a previous SARS-CoV-2 infection and 59 recent vaccine recipients were against the Delta variant, compared with the Alpha and Beta variants, and a reference variant that is more similar to earlier strains of SARS-CoV-2. The authors found that some monoclonal antibodies — including the treatment bamlanivimab — were unable to bind to the spike protein of the Delta variant, which prevented these monoclonal antibodies from neutralizing the virus. The findings suggest that the Delta variant manages to escape antibodies that target certain parts of the spike protein.

The authors also showed that the Delta variant was fourfold less sensitive than the Alpha variant to sera collected from individuals who had recovered from COVID-19 up to 12 months after SARS-CoV-2 infection. A single dose of either the Pfizer–BioNTech or the AstraZeneca COVID-19 vaccines was poorly or not at all efficient against the Beta and Delta variants; only about 10% of individuals were able to neutralize the Delta variant after one dose. However, administration of a second dose of either vaccine generated a neutralizing response in 95% of the individuals, although the antibodies were found to be three-to-fivefold less potent against the Delta variant than the Alpha variant. The authors also found that vaccination of individuals with a previous SARS-CoV-2 infection boosted immunity above the threshold for neutralization of the variant.