In order to further investigate the role of C5a in COVID-19 pathogenesis, we calculated the ratios of C5a to several blood indices and found that ratios of C5a to lymphocyte (Figure 3K), RBC (Figure 3L), Hgb (Figure 3M), Hct (Figure 3N), albumin (Figure 3O), and calcium (Figure 3P) were significantly higher in severe patients in comparison with patients with no or mild symptoms (Figure 3 and Supplementary Table 2). Here, C5AR1 is linked to COVID-19.