Replication and immune evasion of the SARS-CoV-2B.1.617.2 delta variant

Mlcochova, P., Kemp, S., Dhar, MS etal. Replication and immune evasion of the SARS-CoV-2B.1.617.2 delta variant. Nature (2021). https://doi.org/10.1038/s41586-021-03944-y

Commentary

The SARS-CoV-2 B.1.617.2 (Delta) variant is spreading in a manner that outcompetes existing strains such as B.1.617.1 (Kappa) and B.1.1.

In vitro, B.1.617.2 was one-sixth as susceptible to serum neutralizing antibodies and one-eighth as susceptible to vaccine-induced antibodies from recovered individuals as compared to wild-type (WT) Wuhan-1 harboring D614G.

Serum neutralization titers against B.1.617.2 were lower in ChAdOx-1 and BNT162b2 vaccinees, and the B.1.617.2 spike pseudotype virus showed reduced susceptibility to monoclonal antibodies against the receptor binding domain (RBD) and N-terminal domain (NTD).

B.1.617.2 showed higher replication efficiency in both airway organoids and human airway epithelial system compared to B.1.1.7. This indicates that B.1.617.2 is mainly associated with B.1.617.2 spikes in the truncated state compared to B.1.1.7.

The spike protein is less sensitive to inhibition by neutralizing antibodies than the WT spike and mediates very efficient syncytium formation, and we observed that B.1.617.2 has more replication and spike-mediated invasion compared to B.1.617.1.

This may explain the superiority of B.1.617.2. Analyzing more than 130 SARS-CoV-2 infected healthcare workers in three centers in India during the mixed strain circulation, we observed that the efficacy of ChAdOx-1 vaccine against B.1.617.2 compared to non-B.1.617.2 We observed that the efficacy of ChAdOx-1 vaccine against B.1.617.2 was decreased compared to non-B.1.617.2. 

This warns of the possibility of residual confounding.

The decline in vaccine efficacy against the highly-competent and immune-evading B.1.617.2 appears to warrant continued infection control measures in the post-vaccination era.