AstraZeneca clots mimics Heparin Induced Thrombocytopenia Vaccination with ChAdOx1 nCov-19 can result in the rare development of immune thrombotic thrombocytopenia mediated by platelet-activating antibodies against PF4, which clinically mimics autoimmune heparin-induced thrombocytopenia.
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https://www.nejm.org/doi/full/10.1056/NEJMoa2104840