ACE2 and infection: Given the strong correlations between ACE2 displacement and viral neutralization activities observed in our study against the wild-type strain (overall Spearman’s ρ = 0.84, p < 0.0001; Supplementary Fig. 2), these results suggest that vaccine-elicited humoral responses may be less able to prevent infection by the Delta variant, which is consistent with a recent report showing reduced ability of plasma from convalescent and vaccinated individuals to neutralize this strain57.