PF4 and deep vein thrombosis: As per the American Society of Hematology guidelines for VITT diagnostic criteria, we ascribed the thrombosis to vaccine administration due to the symptoms-onset time window, the past medical history of our patient showed no significant inherited or acquired coagulopathies, the occurrence of both thrombocytopenia (platelet count < 150 × 109/L), the markedly elevated D-dimer (more than four times the upper limit of normal), and the presence of serum antibodies against platelet factor 4 on ELISA assay.