In late February 2021, the first cases of vaccine-induced thrombosis and thrombocytopenia (VITT) were observed in patients after immunization with the ChAdOx1 nCoV-19 adenoviral vector vaccine (Oxford, AstraZeneca) against SARS-CoV-2.1 This prothrombotic response is presumed to be mediated by anti-platelet factor 4 (PF4) antibodies that activate platelets and induce activation and extracellular traps formation of neutrophils.2 These antibodies can also be seen in autoimmune heparin-induced thrombocytopenia, but all the described cases had no previous exposure to heparin.
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