Immune Thrombotic Thrombocytopenia Linked to the AstraZeneca COVID-19 Vaccine

Reports of thrombotic events following the first dose of the AstraZeneca COVID-19 vaccine recently surfaced. Now, two groups provide evidence of a new syndrome, vaccine-induced immune thrombotic thrombocytopenia (VITT).

Greinacher and colleagues described 11 patients in Germany and Austria (median age, 36) who developed severe thrombotic events (primarily portal, splenic, and upper mesenteric vein thrombosis, cerebral vein thrombosis, and pulmonary emboli) with concurrent thrombocytopenia within 16 days of the first dose of vaccine. Five patients went on to develop disseminated intravascular coagulation, and 6 died. Although none had received heparin, the similarity of these events to autoimmune heparin-induced thrombocytopenia (aHIT) prompted testing for platelet-activating antibodies targeting platelet factor 4 (PF4)–heparin using platelet activation and enzyme-linked immunosorbent assays (ELISA). All available serum samples tested positive on both assays. In addition, 24 individuals with suspected venous thrombotic disease after vaccination tested positive on ELISA, and serum from 22 of these individuals also caused platelet activation with the addition of PF4.

Schultz and colleagues reported 5 cases (3 fatal) in healthcare workers (age range, 32–54) who developed severe thrombotic events and thrombocytopenia 7 to 10 days after receiving the first dose of vaccine (among 132,686 persons in Norway who had received one dose). All 5 patients had high IgG antibody levels against PF4-polyanion complexes, and platelets from 4 patients showed activation. No patients had antibodies to SARS-CoV-2 nucleocapsid protein, making prior COVID-19 infection unlikely.