PROS1 and COVID-19: Markedly, C1 nAbs isolated from the overwhelming majority of convalescent individuals recognized antigenic site S1, and potently and specifically inhibited SARS-CoV-2 infection by blocking S protein attachment to ACE2, revealing that site S1 is an immunodominant antigenic site in SARS-CoV-2 RBD that efficiently elicits a strong NAb response during natural SARS-CoV-2 infection (Figures 3B, F and Figure S12A).