Indeed, under the pressure of host immunity, some mutations, which have occurred in the RBD, such as N501Y, K417N, and E484K, are found in numerous variants, including B.1.1.248 and B.1.351 dominant variants.7,8 These mutations may play important roles in increasing viral fitness or were shown to reduce the neutralizing efficacy of RBD-specific antibodies.13–16 These alarming facts call for the development of broad-spectrum inhibitors targeting conserved sites in the S protein to block infection by original SARS-CoV-2 as well as its emerging variants.17 Here, PROS1 is linked to infection.