DEEP VEIN THROMBOSIS; This spontaneous report received from a consumer concerned a 49 year old male. The patient's weight was 80.3 kilograms, and height was 182.9 centimeters. The patient's past medical history included post-operative deep vein thrombosis (more than 30 years ago), depression, heart murmur, and back surgery, and his concurrent conditions included non-smoker, no alcohol use, and marijuana abuse. The patient had no history of known allergies. The patient's mother had a history of aneurysm.  The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin not reported, batch number: unknown, and expiry date: unknown) dose was not reported, administered on 08-APR-2021 for prophylactic vaccination. The batch number was not reported and has been requested. Concomitant medications included fexofenadine hydrochloride (Allegra) for allergy, rivaroxaban (Xarelto) for venous thromboembolism, and omeprazole (Prilosec) for unknown indication. About one and half weeks after vaccination, on 21-APR-2021, the patient was taken to the emergency department and was admitted with the complaints of leg pain since 2 days with suspected blood clot in leg. Over the last days, patient's left leg looked swollen compared to the right leg. The patient also had pain, initially started in groin area and radiated down across the anterior portion of the leg, then to posterior leg, and into toes. The patient also had some intermittent tingling in toes. The patient denied of weakness, numbness or persistent paresthesia. The patient was concerned regarding the pain as it felt similar to the post-operative deep vein thrombosis he had in the past. The patient had been anxious since vaccination when hearing about the development of blood clots. The patient also denied of fevers, chills, chest pain, shortness of breath abdominal pain, nausea, vomiting, diarrhea, and difficulty walking. On 21-APR-2021 16:25, the patient's laboratory data included: Blood pressure (148/66 mmHg), Body mass index (24), Body temperature (98.8 F), Oxygen saturation (100 %) Pulse rate (88), and Respiratory rate (16). On 21-APR-2021 16:32, laboratory data included: Blood pressure (148/66 mmHg), Body temperature (97.8 F), Oxygen saturation (100 %), Pulse rate (91), and Respiratory rate (15). Other general physical examinations included: General: Well-developed well-nourished in no acute distress. HEENT (Head, Eye, Ear, Nose, Throat) examination:  normocephalic atraumatic extra ocular motions are intact. Neck examination: Supple without jugular vein distention or meningismus. Lung examination: Clear auscultation bilaterally without wheezes rales or rhonchi. Heart examination: Regular rate and rhythm without murmurs rubs or gallops. Abdomen examination: Soft no tender non-distended without rebound or guarding. Extremities: Without clubbing cyanosis edema, no lacerations or abrasions or ecchymosis noted, no appreciable size difference in the left leg compared to the right, the patient had some tenderness throughout palpation of the medial thigh on the left with radiation up into the left inguinal region, no calf tenderness or swelling, no erythema, palpable posterior tibialis pulse. Skin examination: Warm and dry and well perfused. Psych examination: Appropriate mood and affect. Neuro examination: Cranial nerves 2-12 are grossly intact, strength is 5/5 in upper and lower extremities, full distal sensation in the left lower extremity, full plantar and dorsiflexion of the left foot including the left great toe, sensation is grossly intact, awake, alert and oriented x3.  On ultrasound Doppler venous lower extremity test, identified sub occlusive thrombus in the left superficial femoral veins, likely related to organizing/chronic thrombus, however no prior imaging was available at the institution for comparison, no evidence of occlusive deep vein thrombosis. The final diagnosis was made as Deep Vein Thrombosis (DVT).  At no time the patient had ever endorsed any chest pain/pleuritic pain, shortness of breath or exertional dyspnea. Due to the nature of this clot, a course of anticoagulation was planned. Patient was prescribed with Xarelto at twice daily starting doses, with transition to 20 mg doses. During the initiation of treatment, the patient should be followed up by his primary care physician for further evaluation. The patient stated that he would call the primary care physician in the following morning for follow-up appointment. The patient was discharged from the hospital on APR-2021. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The outcome of deep vein thrombosis was not reported. This report was serious (Hospitalization Caused / Prolonged, and Other Medically Important Condition).; Sender's Comments: V0: 20210457179-Covid-19 vaccine ad26.cov2.s-deep vein thrombosis. This event is considered not related. The event has a compatible/suggestive temporal relationship, is unlabeled, and has unknown scientific plausibility. There are other factors more likely to be associated with the event than the drug. Specifically: MEDICAL HISTORY