Interestingly, Ladikou et al. have reported that patients with severe COVID-19 who developed venous thromboembolism had highly elevated levels of von Willebrand factor (vWF) and coagulation factor VIIIc29, whose serum levels are correlated with the ABO system and are higher in non-O individuals30,31. Here, VWF is linked to venous thromboembolism.