B.1.617.3 SARS CoV-2 spike E156G/Δ157-158 mutations contribute to reduced neutralization sensitivity and increased infectivity

SARS CoV-2 variants raise significant concerns due to their ability to cause vaccine breakthrough infections. Here, we sequence-characterized the spike gene, isolated from a breakthrough infection, that corresponded to B.1.617.3 lineage. Delineating the functional impact of spike mutations using reporter pseudoviruses (PV) revealed that N-terminal domain (NTD)-specific E156G/{Delta}157-158 contributed to increased infectivity and reduced sensitivity to ChAdOx1 nCoV-19 vaccine (Covishield)-elicited neutralizing antibodies. A six-nucleotide deletion (467-472) in the spike coding region introduced this change in the NTD. We confirmed the presence of E156G/{Delta}157-158 in the RT-PCR-positive cases concurrently screened, in addition to other circulating spike (S1) mutations like T19R, T95I, L452R, E484Q, and D614G. Notably, E156G/{Delta}157-158 was present in more than 85% of the sequences reported from the USA, UK, and India in August 2021. The spike PV bearing combination of E156G/{Delta}157-158 and L452R further promoted infectivity and conferred immune evasion. Additionally, increased cell-to-cell fusion was observed when spike harbored E156G/{Delta}157-158, L452R, and E484Q, suggesting a combinatorial effect of these mutations. Notwithstanding, the plasma from a recovered individual robustly inhibited mutant spike PV, indicating the increased breadth of neutralization post-recovery. Our data highlights the importance of spike NTD-specific changes in determining infectivity and immune escape of variants.