PF4 and Hypofibrinogenemia: Reports from research groups in Norway, Germany, and the United Kingdom have described cases of consumptive coagulopathy in patients following adenoviral vector vaccination, presenting with thrombocytopenia, hypofibrinogenemia, and elevated D-dimer levels, along with incidents of cerebral venous sinus thrombosis associated with anti-platelet factor 4 (PF4) IgG antibodies [48,49,50].