Case 1 A 44‐year‐old man presented with fevers, fatigue, head fogginess and abdominal discomfort on day 8 after ChAdOx1 nCov‐19 vaccination. His platelet count was 70 × 109/L (reduction to 17 × 109/L within 12 hours; reference interval, 150–400 × 109/L), D‐dimer level was 114 mg/L (upper limit of normal [ULN], 0.5 mg/L) and fibrinogen level was normal. Radiology showed portal splenic and mesenteric thrombosis. The patient was treated as probable vaccine‐induced immune thrombotic thrombocytopenia (VITT). Treatment was immediately initiated with intravenous immunoglobulin (IVIg) and anticoagulation with fondaparinux. Anticoagulation changed to bivalirudin when surgery was required. Confirmatory investigations supported a diagnosis of VITT with a positive enzyme‐linked immunosorbent assay (ELISA) result and serum/plasma induced platelet activation on functional assay testing. VITT was confirmed. 10 Case 2 A 46‐year‐old woman with a history of quiescent systemic lupus erythematosus presented 4 days after ChAdOx1 nCov‐19 vaccination with investigations consistent with proximal deep vein thrombosis and bilateral pulmonary emboli without evidence of right heart strain. Her platelet count was 97 × 109/L and D‐dimer level was 1.35 mg/L (ULN, 0.25 mg/L); her fibrinogen level was normal. She was treated as probable VITT, immediately anticoagulated with fondaparinux and received one dose of IVIg 1 mg/kg. Her platelet count was stable during hospitalisation. Confirmatory investigations returned negative ELISA and functional assay results and a positive lupus anticoagulant result. She was deemed to have venous thromboembolism secondary to antiphospholipid syndrome, not VITT, and was changed to standard low molecular weight heparin anticoagulation. VITT was not supported. Case 3 A 60‐year‐old man smoker presented with chest pain and dyspnoea on day 15 after receiving ChAdOx1 nCov‐19, and was found to have bilateral pulmonary emboli without haemodynamic compromise or right heart strain. His platelet count was 228 × 109/L and D‐dimer level was 0.6 mg/L (ULN, 0.5 mg/L); his fibrinogen level was normal, and his baseline platelet count was 235 × 109/L. He was treated as much less likely to have VITT (based on normal platelet count), and apixaban was commenced at standard dosing. A repeat platelet count 3 days later was stable and confirmatory testing for VITT did not proceed. VITT was not supported. Case 4 A 50‐year‐old woman presented with extensive petechiae and oral mucosal wet purpura 4 days after ChAdOx1 nCov‐19 vaccination. No symptoms of thrombosis were present on system review. She had no previous history of idiopathic thrombocytopenic purpura or autoimmune disease. Her platelet count was 3 × 109/L and D‐dimer level was 1.25 mg/L (ULN, 0.25 mg/L); her fibrinogen level was normal. She was treated as less likely VITT based on normal D‐dimer levels and lack of thrombosis. She was diagnosed with idiopathic thrombocytopenic purpura, likely vaccine associated, and commenced IVIg 2 g/kg divided over 2 days, with dexamethasone 40 mg daily for 4 days. Her platelet count improved to 50 × 109/L on day 2. Non‐urgent VITT testing supported a diagnosis of not VITT with a negative ELISA result. VITT was not supported. Case 5 An 82‐year‐old man with prostate cancer presented with dyspnoea 17 days after receiving ChAdOx1 nCov‐19. He had a background of inflammatory bowel disease and was found to have sub‐massive pulmonary emboli. His platelet count was 198 × 109/L, D‐dimer level was 9.8 mg/L (ULN, 0.25 mg/L) and fibrinogen level was normal. He was treated as less likely to have VITT (normal platelet count, markedly raised D‐dimer), and commenced therapeutic fondaparinux. Confirmatory investigations did not support a diagnosis of VITT, with a negative ELISA immunoassay, and he did not progress to functional testing. His treatment was changed to low molecular weight heparin and he was discharged on a direct oral anticoagulant when he was stable. VITT was not supported.

* Case 1 summarises a published case: Hocking et al. ¹⁰ Other vignettes are hypothetical and do not refer to specific individuals.