The C5a (7,770.3 ± 191; p =0.0047), C3a (5,019.2 ± 920.4; p = 0.0008), and factor P (68.8 ± 6.7; p = 0.0002) concentrations were significantly higher in the critical COVID-19 non-survival group than in the critical COVID-19 survival group (Figure 5). Here, C3 is linked to COVID-19.