In addition, researchers confirmed that the furin cleavage sites (FCSs; aa 681 to 685; aa sequence: PRRAR) of the S protein might facilitate the SARS-CoV-2 to be more contagious (19, 20), and numerous researchers have characterized that SARS-CoV-2 FCS deletion mutants significantly attenuated viral infection (21, 22). This evidence concerns the gene PROS1 and viral infectious disease.