ACE2 and infection: Consistent with the more efficient replication of B.1.351 in donor Vero-ACE2 cells over the entire 26-h infection period (Q3 in Fig. 7 A, Upper), we found a significantly higher cell-free infectivity for B.1.351 produced during the initial 20-h infection relative to WT, D614G, and B.1.1.7 (Fig. 7D, see “no sera”).