ACE2 and infection: Similar to IgG concentrations, a SARS-CoV-2 breakthrough infection markedly boosted wild-type-specific and BA.1-specific ACE2 displacement activities at both 3 and 6 months post-third dose (all P < 0.0001), where activities at 6 months in this group were overall significantly greater than peak responses induced by three-dose vaccination (both P < 0.0001) (Fig. 2a).