ACE2 and infection: Our results show that recombinant ACE2-Ig protein could inhibit Kappa, Delta, and B.1.618 infection with efficacy comparable to or better than that of the WT (Fig. 5A to D), which is consistent with the results that Kappa, Delta, and B.1.618 spike proteins exhibited increased binding affinity with human ACE2 (Fig. 1B).