PROS1 and COVID-19: Enzyme‐linked immunosorbent assays using anti‐S antibodies showed that threefold higher levels of VLPs containing the full‐length S protein were obtained by infiltration with S alone, compared to co‐infiltration of S with M and E. The S protein within the VLPs could be cleaved by furin in vitro and the particles showed reactivity with serum from recovering COVID‐19 patients, but not with human serum taken before the pandemic.