A recent report in the journal Blood detailed the experiences of 5 patients who developed prothrombotic immune thrombocytopenia after receiving the ChAdOx1 vaccine (AZD1222) against SARS-CoV-2.

In this study, patients were seen at Hannover Medical School in Hannover, Germany, from March 8 to April 4, 2021. In this cohort, patients presented with known or suspected thromboembolic events or thrombocytopenia in the 2 weeks following AZD1222 vaccination. Patients were evaluated for antiplatelet factor 4 (PF4) autoantibodies using enzyme-linked immunosorbent assay (ELISA) and chemiluminescent immunoassay (CLIA) approaches.

Ages among the 5 patients ranged from 41 to 67 years, and all were female. The types of thromboembolic events these patients experienced included cerebral venous sinus thrombosis with evidence of thrombotic microangiopathy (TMA) in 1 patient. Arterial cerebral embolism, transient ischemic attack (TIA), and splanchnic vein thrombosis (SVT) occurred in 1 patient each. One patient experienced arterial cerebral thrombosis and popliteal artery thrombosis.

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All but 1 patient presented with a headache on admission. The patient who had a TIA had a headache with visual disturbance, but imaging revealed no abnormalities. The patient with SVT showed no evidence of thrombosis when she was initially hospitalized, but this thromboembolic event appeared on day 6. The patient with arterial cerebral thrombosis had presented initially with this condition and developed popliteal artery thrombosis on day 8 of the hospital stay.

In all patients, the D-dimer level was increased, and platelet counts indicated thrombocytopenia in all of them. No patients had a history of heparin exposure, and they all demonstrated SARS-CoV-2 negativity by polymerase chain reaction analysis. Tests for the presence of anti-PF4 autoantibodies were negative by CLIA analysis but positive by ELISA analysis for all patients. Patient immunoglobulins showed binding to healthy donor platelets in the presence of AZD1222, but not when heparin was present.

Anticoagulation was given to all patients, in the form of unfractionated heparin in 1 patient and argatroban to all others. Eculizumab or intravenous immunoglobulin was additionally given to 4 patients. Three of the patients reportedly experienced either quick recoveries or a favorable outcome without further events.

“Despite the suggestive temporal relationship between vaccination and the prothrombotic immune thrombocytopenia reported here, caution is required when drawing conclusions about the safety of AZD1222 in the general population,” the study authors concluded in their report.


Tiede A, Sachs UJ, Czwalinna A, et al. Prothrombotic immune thrombocytopenia after COVID-19 vaccination. Blood. 2021;138(4):350-353. doi:10.1182/blood.2021011958