PROS1 and COVID-19: An eightfold higher antibody response to the SARS-CoV-2 S protein was observed in the oldest age group of COVID-19 patients (age >60) compared to the youngest age group (age <35) (4.1 log10 vs. 3.2 log10 MFI, p<0.001), which is in line with age being a risk factor for severe COVID-19 (Figure 1a; Williamson et al., 2020).