NOS3 and COVID-19: In this regard, it became necessary to investigate polymorphic variants of the genes fibrinogen beta (FGB, rs1800790), endothelial nitric oxide synthase (NOS3, rs2070744), and transmembrane serine protease 2 (TMPRSS2, rs12329760) in the context of the severity and clinical and laboratory features of COVID-19 in order to identify high-risk groups with a more severe course of the disease and a greater susceptibility to COVID-19, as well as to assess the impact of antiviral therapy.