PROS1 and viral infectious disease: Because the critical antigenic determinants recognized by S2-4D, S2-5D, S2-8D, and S2-4A are located at the immediately upstream region of HR2 (Fig. S3), which is predicted to be located within residues 1162–1205 (35) or 1163–1211 of the SARS-CoV-2 S protein (34), we propose that binding of S2-4D, S2-5D, S2-8D, and S2-4A to this region can prevent the S2 subunit from forming a six-helix bundle core of HR1 and HR2, leading to blockage of membrane fusion and virus infection.