PROS1 and COVID-19: Although both cellular and humoral immune responses play important roles in preventing COVID-19 infection, it is generally believed that the higher the titer of neutralizing antibodies, the better the protective effect against COVID-19.26,27 In this study, using Alpha-, Beta-, Gamma- and Delta-derived S protein-immunized animal sera, the neutralization activities were mostly reduced within fourfold against the current VOCs and VOIs.