C5 and COVID-19: However, based on known high levels of C5a and neutrophil activation in COVID-19 and the presence of neutrophil extracellular trap (NET)osis in the microvasculature [8, 27, 28], i.e., microthrombosis which contributes to mortality [28], significant improvement in survival of critically ill, invasively mechanically ventilated COVID-19 patients with vilobelimab are consistent with its presumed PD effect [1].