Regarding the possibility of inducing cross-neutralizing antibodies by immunizing mice with the SARS-CoV RBD, several studies have indicated that natural infection with SARS-CoV or SARS-CoV-2 and immunization of animals with the SARS-CoV RBD induced very limited cross-neutralizing S protein-targeting antibody responses,26,27 which is consistent with our observation. Here, PROS1 is linked to infection.