Thrombotic Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination

Key findings: • 11 patients presented with one or more thrombotic events beginning 5-16 days after vaccination: o 9 had cerebral venous thrombosis, 1 had intracranial hemorrhage, and 5 had disseminated intravascular coagulation. o 6 patients died. • Serum samples from a subset (n = 4), showed platelet reactivity was inhibited by low-molecular-weight heparin and greatly enhanced by platelet factor 4 (PF4) (Figure). o None received any heparin prior to presentation.