C5 and COVID-19: According to the procedure for the selection of studies described in the Methods section and in boxes 1–4 in Figure 3, we selected one study on C5a/C5aR1 [8] and two studies on antibodies [26,29] in COVID-19 patients from 2012 studies in the literature selected from the PMC (PubMed Central®) databases with the keywords (((COVID-19) AND individual) NOT review) AND C5a/IgG.