VACCINE INDUCED IMMUNE THROMBOTIC THROMBOCYTOPENIA (VITT)/SPONTANEOUS HITT; THROMBOCYTOPENIA; EXTENSIVE OCCLUSIVE DEEP VEIN THROMBOSIS OF THE LEFT SUPERFICIAL FEMORAL POPLITEAL POSTERIOR TIBIAL AND PERONEAL VEINS; OCCLUSIONS OF BILATERAL ILIAC AND SUPERFICIAL FEMORAL ARTERIES; NORMOCYTIC ANEMIA; This spontaneous report was received from literature. This report concerned a 59 year old female. The report introduces vaccine induced thrombocytopenic thrombosis (VITT) after COVID-19 vaccination which is a rare complication previously noted in the AstraZeneca vaccine and more recently with Johnson & Johnson's vaccine. Both vaccines use a Viral-Vector for delivery. The patient's height, and weight were not reported. The patient's past medical history included: uneventful covid-19 infection in January, and concurrent conditions included: coronary artery disease, hypertension, chronic obstructive pulmonary disease and tobacco user. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin, and batch number were not reported, expiry: UNKNOWN) dose, start therapy date were not reported, 1 total administered for prophylactic vaccination. The batch number was not reported. The Company is unable to perform follow-up to request batch/lot numbers. No concomitant medications were reported.  On an unspecified date, the patient was presented to Urgent Care with a complaint of 5 days of progressive left leg swelling with associated pain and erythema. The patient had no recent illness, immobility or injury. It was reported that the patient was vaccinated with Johnson & Johnson COVID-19 vaccine administered just 10 days prior to symptom onset. She was transferred to the hospital Emergency Department for evaluation of suspected deep vein thrombosis (DVT). Venous Doppler of the left leg was performed in the emergency department which was found to have extensive occlusive DVT of the left superficial femoral, popliteal, posterior tibial, and peroneal veins. The initial labs were significant for thrombocytopenia with a platelet count of 15 x10E3/units per litre (U/L), International normalized ratio (INR) of 1.3 with low fibrinogen and high fibrin degradation products and elevated Lactate dehydrogenase (LDH) of 704 U/L. It was reported that the patient was unable to treat with anticoagulation for DVT, hence an inferior vena cava (IVC) filter was placed and she was hospitalized. Early the next morning the patient began experiencing loss of sensation in the right foot. An Arterial Doppler of the right leg was performed which was significant for high-grade occlusion of the right proximal superficial femoral artery. The patient was emergently taken to the cath lab where abdominal aortogram showed occlusions of bilateral iliac and superficial femoral arteries. Bilateral thrombectomy and stents were placed in both iliac arteries. Hematology was consulted for what appeared to be HITT (Heparin induced thrombotic thrombocytopenia) reaction despite no heparin exposure and treatment with Bivalirudin was initiated. A peripheral blood smear noted thrombocytopenia with normocytic anemia, but no schistocytes were seen. Heparin-induced thrombocytopenia (HIT) panel was positive HIT antigen on Platelet factor 4 (PF4) and positive serotonin release assay (SRA), with an optical density (OD) of 0.519. There was no further clot formation occurred during the patient's hospitalization and platelet count improved after initiation of bivalirudin. The duration of hospitalization was unspecified. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient was recovering from thrombocytopenia, and the outcome of normocytic anemia, extensive occlusive deep vein thrombosis of the left superficial femoral, popliteal, posterior tibial and peroneal veins, vaccine induced immune thrombotic thrombocytopenia (VITT)/spontaneous HITT and occlusions of bilateral iliac and superficial femoral arteries was not reported. In conclusion, considering VITT for thrombocytopenia and thrombosis within 2 weeks after COVID-19 vaccination may be beneficial in earlier treatment with bivalirudin to prevent further vascular occlusions. This report was serious (Hospitalization Caused / Prolonged).; Sender's Comments: V0: 20211023115-covid-19 vaccine ad26.cov2.s- vaccine induced immune thrombotic thrombocytopenia (VITT)/spontaneous HITT, thrombocytopenia, extensive occlusive deep vein thrombosis of the left superficial femoral, popliteal, posterior tibial and peroneal veins, occlusions of bilateral iliac and superficial femoral arteries. This event(s) is labeled per agency and is therefore considered potentially related.  20211023115-covid-19 vaccine ad26.cov2.s.-Normocytic anemia. This event(s) is considered unassessable. The event(s) has a compatible/suggestive temporal relationship, is unlabeled, and has unknown scientific plausibility. There is no information on any other factors potentially associated with the event(s).