PROS1 and COVID-19: IgG binding to the S protein of the ancestral lineage (3622.4-fold increase over pre-D1; p< 0.0001), S protein from the Delta variant (1122.0-fold increase over pre-D1; p< 0.0001), and the S protein from the Omicron BA.1 variant (1336.6-fold increase over pre-D1; p< 0.0001) were significantly elevated following D2 of the COVID-19 mRNA vaccines (Figure 1A).