PF4 and Thrombocytopenia: From the clinical and laboratory characteristics of 11 recipients of ChAdOx1 nCov-19 vaccine who developed thrombosis or thrombocytopenia in Austria and Germany, Greinacher et al. [18] concluded that platelet-activating antibodies PF4 mediates a rare development of immune thrombotic thrombocytopenia (ITT), following vaccination with ChAdOx1 nCov-19.