PF4 and Venous thrombosis: CVT occurring after adenoviral vector-based SARS-CoV-2 vaccines6,7 is often associated with thrombocytopenia and the pathophysiology of thrombosis has been postulated to be due to vaccine-induced immune thrombotic thrombocytopenia (VITT).29,30 VITT is a syndrome of thrombosis, in particular of the cerebral venous sinuses, with thrombocytopenia and presence of antibodies to PF4.