Severe COVID-19 is characterized by inflammation and coagulation in the presence of complement system activation, resulting from the activation of the complement factor 5a (C5a)/C5a receptor 1 (C5aR1) signaling axis.5,6 The potent anaphylatoxin C5a and C5aR1 play a critical role in activating and recruiting neutrophils and monocytes to the infection site, causing tissue damage by oxidative radical formation, enzyme release, and induction of NETosis. Here, C5AR1 is linked to COVID-19.