Thrombotic Thrombocytopenia after ChAdOx1 nCov-19 Vaccination

Abstract (PubMed)

Several cases of unusual thrombotic events and thrombocytopenia have developed after vaccination with ChAdOx1 nCov-19 (AstraZeneca). We assessed the clinical and laboratory features of 11 patients in Germany and Austria in whom thrombosis or thrombocytopenia had developed after vaccination. We used ELISA to detect platelet factor 4 (PF4)-heparin antibodies and a modified platelet-activation test to detect platelet-activating antibodies. Of the 11 original patients, 9 were women, with a median age of 36 years. Beginning 5 to 16 days after vaccination, the patients presented with one or more thrombotic events. Of the patients with thrombotic events, 9 had cerebral venous thrombosis, 3 had splanchnic-vein thrombosis, 3 had pulmonary embolism, and 4 had other thromboses; 6 died. The patients had thrombocytopenia, with platelet counts ranging from 9000 to 107,000 per cubic millimeter. All 28 patients tested positive for antibodies against PF4-heparin on ELISA. The platelet-activation test confirmed platelet-activating antibodies in 22 patients. This disorder — vaccine-induced immune thrombocytopenia and thrombosis (VITT) — is caused by platelet-activating antibodies against PF4, which is similar to autoimmune heparin-induced thrombocytopenia.