Using a flow cytometry-based assay to detect antibodies against full-length S protein (SFB assay) (Goh et al., 2021a,b), we first examined if IgM, IgA and IgG against the ancestral wildtype (WT) S protein were associated with disease severity (n = 81; Supplementary Table S1) over the early course of infection, at time-points median 5-, 10-and 23-days post-illness onset (pio). This evidence concerns the gene PROS1 and infection.