Enhanced fusogenicity and pathogenicity of SARS-CoV-2 Delta P681R mutation.

During the current SARS-CoV-2 pandemic, a variety of mutations have accumulated in the viral genome, and currently, four variants of concern (VOCs) are considered potentially hazardous to human society1. The recently emerged B.1.617.2/Delta VOC is closely associated with the COVID-19 surge that occurred in India in the spring of 20212. However, its virological properties remain unclear. Here, we show that the B.1.617.2/Delta variant is highly fusogenic and notably more pathogenic than prototypic SARS-CoV-2 in infected hamsters. The P681R mutation in the spike protein, which is highly conserved in this lineage, facilitates spike protein cleavage and enhances viral fusogenicity. Moreover, we demonstrate that the P681R-bearing virus exhibits higher pathogenicity than its parental virus. Our data suggest that the P681R mutation is a hallmark of the virological phenotype of the B.1.617.2/Delta variant and is associated with enhanced pathogenicity.