Discussion

Thrombocytopenia and thrombotic complications at unusual sites may develop around 1–2 weeks after the first vaccine dose of ChAdOx1 nCov-19. The incidence is still not well-known but it appears to be extremely rare. 1 Clinicians should be aware that a syndrome similar to autoimmune heparin-induced thrombocytopenia may occur in very few persons after exposure to the ChAdOx1 nCoV-19 vaccines. However, these vaccinated patients did not receive any heparin to explain the subsequent occurrence of thrombosis and thrombocytopenia. In all cases reported to date, this syndrome of thrombocytopenia and venous thrombosis appears to be triggered by receipt of the first dose of the vaccine. 1–3 The pathomechanism is presumably the formation of antibodies against PF4, causing platelet consumption with thrombocytopenia and thrombus formation. 3–5 Whether these anti-PF4 autoantibodies induced by the strong inflammatory stimulus of vaccination or caused by the vaccine that cross-react with PF4 and platelets requires further investigation. 1–3 Administration of high-dose intravenous immunoglobulin (1 g/kg daily for 2 days) or dexamethasone (40 mg days for 4 days) may be useful to interrupt the prothrombotic mechanism. 4 Use of direct oral anticoagulants is also suggested. In these patients, platelet transfusions should not be transfused in the absence of bleeding. Anticoagulation with unfractionated heparin or low molecular weight heparin should be avoided. 3–5