Despite the variability of the S protein, we identified a relatively conserved site (Fig. 2D) that corresponds to a fusion peptide adjacent to the S2’ cleavage site (Madu et al., 2009) that is also the most cross-reactive epitope among naïve and COVID-19 patients (Shrock et al., 2020) (Fig. 4C). Here, PROS1 is linked to COVID-19.