Timeline from presentation of first symptoms 8 days after vaccination with the ChAdOx1 nCoV-19 vaccine to outpatient postvaccination follow-up day 35. Serial coagulation test results are shown: platelet counts, D-dimer, and fibrinogen. Time points for the result of the anti-PF4 antibody test and key clinical events, including timing of thrombosis events and changes in anticoagulant treatment, are also shown. ED, emergency department; MRI, magnetic resonance imaging; ELISA, enzyme-linked immunosorbent assay; HIPA, heparin-induced platelet activation; FEU, fibrinogen equivalent units.