a, Phylogenetic tree of SARS-CoV-2 variants, with B.1.351 and B.1.1.7 highlighted. b, Mutations in the viral spike protein identified in B.1.351 (SA) and B.1.1.7 (UK) in addition to D614G. c, Titres of wild-type (D614G) and 18 mutant SARS-CoV-2 pseudoviruses. VSV-based pseudoviruses were generated20,21 and viral particles were quantified and normalized to the expression of the nucleocapsid protein of VSV by western blot. Equal amounts of each pseudovirus were then used to infect Vero E6 cells and relative luciferase units (RLUs) were measured 16 h later. Data are mean ± s.e.m. of technical duplicates.