To contextualize the isolate of the Delta variant reported here, we inferred a global phylogeny by subsampling the diversity of SARS-CoV-2 sequences available on the GISAID EpiCoV database (Extended Data Fig. Future work will help to determine whether Delta is more fusogenic than other variants, as suggested here by the large size of Delta-induced syncytia. Large syncytia expressing the spike protein were observed in cells that were infected with the Delta variant (Extended Data Fig. The viral titres were similar in the two target cells and reached 10 5–10 6 infectious units per ml. Viral stocks were titrated using S-Fuse reporter cells and Vero cells 10, 11. This set of mutations was different from that observed in other members of the B.1.617 lineage and other VOCs (Extended Data Fig. When compared to the D614G strain (belonging to the basal B.1 lineage), which was used here as a reference, the spike protein contained eight mutations, including four mutations in the NTD (T19R, G142D, Δ156–157 and R158G), two in the RBD (L452R and T478K), one mutation close to the furin-cleavage site (P681R) and one in the S2 region (D950N) (Extended Data Fig. Sequences of the swab and the outgrown virus were identical, and identified the Delta variant (GISAID accession ID: EPI_ISL_2029113) (Extended Data Fig. The virus was amplified by two passages on Vero E6 cells. We isolated the Delta variant from a nasopharyngeal swab of a symptomatic individual a few days after his return to France from India. Thus, the spread of the Delta variant is associated with an escape from antibodies that target non-RBD and RBD epitopes of the spike protein. Administration of two doses of the vaccine generated a neutralizing response in 95% of individuals, with titres three- to fivefold lower against the Delta variant than against the Alpha variant. Sera from individuals who had received one dose of the Pfizer or the AstraZeneca vaccine had a barely discernible inhibitory effect on the Delta variant. Sera collected from convalescent individuals up to 12 months after the onset of symptoms were fourfold less potent against the Delta variant relative to the Alpha variant (B.1.1.7). The Delta variant was resistant to neutralization by some anti-NTD and anti-RBD monoclonal antibodies, including bamlanivimab, and these antibodies showed impaired binding to the spike protein. We examined the sensitivity of this strain to monoclonal antibodies and to antibodies present in sera from individuals who had recovered from COVID-19 (hereafter referred to as convalescent individuals) or who had received a COVID-19 vaccine, and then compared this strain with other strains of SARS-CoV-2. Here we isolated an infectious strain of the Delta variant from an individual with COVID-19 who had returned to France from India. B.1.617.2-also termed the Delta variant-is believed to spread faster than other variants. The lineage includes three main subtypes (B1.617.1, B.1.617.2 and B.1.617.3), which contain diverse mutations in the N-terminal domain (NTD) and the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein that may increase the immune evasion potential of these variants. Since then, it has become dominant in some regions of India and in the UK, and has spread to many other countries 6. The SARS-CoV-2 B.1.617 lineage was identified in October 2020 in India 1, 2, 3, 4, 5. Nature volume 596, pages 276–280 ( 2021) Cite this article Reduced sensitivity of SARS-CoV-2 variant Delta to antibody neutralization
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