COLD SYMPTOMS; DECREASED PLATELET COUNT; SADDLE PULMONARY EMBOLUS; BLOOD CLOT IN RIGHT LEG; This spontaneous report was received from a physician, and concerned a 58 year-old male patient. Initial report was processed along with additional information received on 16-APR-2021. The patient's height was 76 inches, weight was 266 pounds, body mass index 32.4. The patient's concurrent conditions included hypertension, and non-smoker. The patient had no personal or family history of clotting disorders, no recent trauma or travel. He had an active lifestyle (an outdoorsman who cut his own firewood). The patient received Covid-19 vaccine Ad26.COV2.S (suspension for injection, route of admin not reported, batch/lot number: 1808609) dose was not reported, administered on 02-APR-2021 vaccine anatomical site unknown, for prophylactic vaccination. Concomitant medications included hydrochlorothiazide for hypertension.  On 03-APR-2021, the patient experienced cold symptoms. It was reported that some days later, he developed shortness of breath, dyspnea on exertion, decreased exercise tolerance and right calf swelling.  On 13-APR-2021, the patient went to the doctor's office for his symptoms. An electrocardiogram (EKG) was normal, and the ultrasound of right leg revealed a blood clot. As the patient preferred to keep costs down, he was not hospitalized and was started on anticoagulant Eliquis (apixaban). He was not hypoxic. On 14-APR-2021, he called the doctor after a syncopal episode and was advised to go to the emergency room (ER) where a computerized tomography (CT) scan showed a saddle pulmonary embolus with evidence of right heart strain. His oxygen (O2) saturation was 97-98%. No treatment was given in the ER as he already had started apixaban (2 doses received by that time). Laboratory data included a normal comprehensive metabolic profile, normal troponin, white blood cell count 9, hemoglobin 16, platelet count 120 (lower limit normal: 130). No other tests were performed, and no prior complete blood count (CBC) was available. On 16-APR-2021, the doctor called the patient for follow up, and noted that he was feeling better. Action taken with Covid-19 vaccine Ad26.COV2.S was not applicable. The outcome of the blood clot in right leg, saddle pulmonary embolus, decreased platelet count, and cold symptoms was not reported. This report was serious (Other Medically Important Condition).; Sender's Comments: V0: This 58 year-old obese (BMI 32.4) male was diagnosed with a right leg blood clot and saddle pulmonary embolus 11 and 12 days, respectively after vaccination with the Janssen Covid-19 vaccine. Medical history included hypertension controlled with hydrochlorothiazide. He is a non-smoker who leads an active lifestyle; there was no recent trauma or travel and he had no personal or family history of clotting disorders. The day after the vaccination, he experienced cold symptoms. Then, an unspecified number of days later, he developed right calf swelling, shortness of breath, dyspnea on exertion, and decreased exercise tolerance. Eleven days after vaccination, he went to see his doctor who ordered an ultrasound which revealed a blood clot in his right leg. EKG was normal and he was not hypoxic. Apixaban was started as an outpatient. The following day, the patient called the doctor after a syncopal episode and was advised to go to the emergency room; CT scan revealed a saddle pulmonary embolus with evidence of right heart strain. Oxygen saturation was 97-98%.  Labs included normal comprehensive metabolic profile, troponin, white blood cell count of 9, hemoglobin 16, platelet count 120 (lower limit normal: 130). No treatment was provided in the ER as he had already started apixaban. No other tests were performed, and the patient returned home. Two days later, when his physician called him in follow up, he was reportedly feeling better. Of note, platelet count was not checked on the day of leg thrombosis diagnosis prior to apixaban initiation and no other prior values were available for comparison; thrombocytopenia is a known adverse reaction with apixaban. Based on the available information, the relationship of the blood clot in the leg and pulmonary embolus with Janssen Covid-19 vaccine is considered indeterminant.