ACE2 and COVID-19: The main target of the antigenic epitopes of the COVID-19 vaccine are the S protein [14]; the S1 domain, which contains the receptor-binding domain (RBD) for the host cell receptor angiotensin-converting enzyme-2 (ACE2) [15]; the N-terminal domain (NTD), which has been demonstrated as another site with potent neutralizing activity [16,17,18]; the S2 domain, which contains the fusion peptide [19,20].