The volunteer was a 72-year-old Korean man (weight 62.5 kg; height 168 cm). Vital signs on the day before vaccination were: blood pressure, 120/80 mmHg; pulse rate, 70 beats/min; and body temperature, 36.8 °C. He was diagnosed with diabetes mellitus, hypertension, and hypercholesterolemia at the age of 45 years. His routine medications were atorvastatin (10 mg), aspirin (100 mg), diltiazem (180 mg), and long-acting insulin, which continued throughout the observation period. The baseline laboratory findings are presented in Table. At 3 p.m. on 9 June 2021, the volunteer received the AstraZeneca COVID-19 vaccine (5 mL) in the left deltoid muscle (ChAdOx1-S/nCoV-19 [recombinant] vaccine, CTMAV563). Blood samples were obtained 1 day before vaccination (baseline) and on days 1, 3, 7, 14, and 21 post vaccination. The following parameters were measured in the context of routine testing in a selected general hospital: platelet indices (PI), including mean platelet volume (MPV) and platelet distribution width (PDW), and platelet-large cell ratio (P-LCR) were measured together on a fully automated hematology analyzer (Sysmex XN-1000TM; Sysmex Corp., Kobe, Japan). Thrombin receptor-activating peptide (TRAP)-induced platelet aggregation was measured using a Multiplate® analyzer (Roche Diagnostics GmbH, Mannheim, Germany). Prothrombin time, activated partial thromboplastin time, and D-dimer were measured on the STACompact Max® analyzer (Diagnostica Stago, Asnieres, France). Thrombin–antithrombin III complex (TAT) and plasmin-α2 antiplasmin complex (PAP) assays were outsourced to BioMedical Laboratories, Japan (BML Japan: ). The assay kits used were the HISCL® TAT test kit (Sysmex Corp.) for TAT assessment and the LPIA-NV7 STACIA® test kit (LSI Medicine Corp., Tokyo, Japan) for PAP assessment. Assays for the following parameters were outsourced to EONE Laboratories (Incheon South Korea: ): both von Willebrand factor (vWF) antigen and activity (Instrumentation Laboratory, Bedford, MA, USA); plasminogen activator inhibitor-1 (PAI-1; Asserachrom PAI-1 enzyme immunoassay kit; Diagnostica Stago); protein C and protein S antigen levels (enzyme-linked immunosorbent assay kit; Corgenix Medical Corp., Broomfield, Colorado, USA); protein C activity (synthetic chromogenic substrate method; Stachrom protein C kit; Diagnostica Stago); protein S activity (Factor Va inhibition test kit; Diagnostica Stago); lupus anticoagulant (diluted Russell viper venom test; Diagnostica Stago); fibrinogen degradation product (FDP; antibody-coated latex agglutination kit; Sekisui Medical Co. Ltd., Tokyo, Japan); and plasminogen (synthetic chromogenic substrate method; Stachrom Plasminogen kit; Diagnostica Stago).