Extensive pulmonary embolism; Deep venous thrombosis (DVT)/thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins; Vaccine-induced thrombosis without thrombocytopenia; The patient experienced fatigue, shortness of breath, sore throat, and nausea; The patient experienced fatigue, shortness of breath, sore throat, and nausea; The patient experienced fatigue, shortness of breath, sore throat, and nausea; This literature-non-study case was reported in a literature article and describes the occurrence of PULMONARY EMBOLISM (Extensive pulmonary embolism), DEEP VEIN THROMBOSIS (Deep venous thrombosis (DVT)/thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins) and THROMBOSIS (Vaccine-induced thrombosis without thrombocytopenia) in a 31-year-old male patient who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.       Concurrent medical conditions included Obesity (grade I (BMI): 33 kg/m²).    On an unknown date, the patient received second dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced PULMONARY EMBOLISM (Extensive pulmonary embolism) (seriousness criterion medically significant), DEEP VEIN THROMBOSIS (Deep venous thrombosis (DVT)/thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins) (seriousness criterion medically significant), THROMBOSIS (Vaccine-induced thrombosis without thrombocytopenia) (seriousness criterion medically significant), OROPHARYNGEAL PAIN (The patient experienced fatigue, shortness of breath, sore throat, and nausea), FATIGUE (The patient experienced fatigue, shortness of breath, sore throat, and nausea) and NAUSEA (The patient experienced fatigue, shortness of breath, sore throat, and nausea). The patient was treated with ENOXAPARIN at a dose of 110 milligram every twelve hours; APIXABAN at a dose of 10 milligram twice a day and APIXABAN at a dose of 5 milligram once a day. At the time of the report, PULMONARY EMBOLISM (Extensive pulmonary embolism), DEEP VEIN THROMBOSIS (Deep venous thrombosis (DVT)/thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins) and THROMBOSIS (Vaccine-induced thrombosis without thrombocytopenia) outcome was unknown and OROPHARYNGEAL PAIN (The patient experienced fatigue, shortness of breath, sore throat, and nausea), FATIGUE (The patient experienced fatigue, shortness of breath, sore throat, and nausea) and NAUSEA (The patient experienced fatigue, shortness of breath, sore throat, and nausea) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Angiogram: found extensive pulmonary emboli in the bilateral main pulmonary, lobar, and segmental arteries with possible mild right heart strain, later confirmed by an echocardiogram. On an unknown date, Antiphospholipid antibodies: Lupus anticoagulant Not detected. On an unknown date, Antithrombin III (75-135): 116 %. On an unknown date, Beta-2 glycoprotein antibody: Beta-2 glycoprotein I Ab, IgG- less than 9 (reference range: 0-20), (unit: GPI IgG units); Beta-2 glycoprotein I Ab, IgM- less than 9 (reference range: 0-32), (unit: GPI IgM units). On an unknown date, Blood electrolytes: unremarkable. On an unknown date, Blood lactic acid: normal. On an unknown date, Blood pressure measurement: 120/80 mmHg. On an unknown date, Body mass index: 33 kilogram per square metre. On an unknown date, Body temperature: 97.7 °F. On an unknown date, Cardiolipin antibody: less than 9 APL U/mL, less than 9 GPL U/mL and less than 9 MPL U/mL. On an unknown date, Computerised tomogram thorax: found extensive pulmonary emboli in the bilateral main pulmonary, lobar, and segmental arteries with possible mild right heart strain, later confirmed by an echocardiogram. On an unknown date, Echocardiogram: extensive pulmonary emboli in the bilateral main pulmonary, lobar, and segmental arteries with possible mild right heart strain, later confirmed by an echocardiogram. On an unknown date, Electrocardiogram: showed a prolonged QT interval and inverted T waves. On an unknown date, Factor V Leiden mutation: No mutation found. On an unknown date, Fibrin D dimer: 5,335 ng/mL D-dimer units (DDU) 5335 ng/mL. On an unknown date, Full blood count: unremarkable. On an unknown date, Heart rate: 78 heart beats per minute. On an unknown date, Heparin-induced thrombocytopenia test (0.000-0.400): 0.045 optical density unit and Negative. On an unknown date, Platelet count: 147 10^9/L. On an unknown date, Protein C (73-180): 78 %. On an unknown date, Protein S (57-157): Protein S free 74 % and Protein S total 120 %. On an unknown date, Respiratory rate: 18 breaths. On an unknown date, Troponin: Negative. On an unknown date, Ultrasound Doppler: Doppler ultrasound of the left lower extremities showed a thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins. On an unknown date, Vital signs measurement: Unremarkable.     For mRNA-1273 (Spikevax) (Unknown), the reporter considered PULMONARY EMBOLISM (Extensive pulmonary embolism), DEEP VEIN THROMBOSIS (Deep venous thrombosis (DVT)/thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins) and THROMBOSIS (Vaccine-induced thrombosis without thrombocytopenia) to be related. No further causality assessments were provided for OROPHARYNGEAL PAIN (The patient experienced fatigue, shortness of breath, sore throat, and nausea), FATIGUE (The patient experienced fatigue, shortness of breath, sore throat, and nausea) and NAUSEA (The patient experienced fatigue, shortness of breath, sore throat, and nausea).    The patient was presented to our emergency department (ED) with a four-day history of left leg swelling and pain in his left knee upon flexion.  Patient had received the second dose of his vaccine one week prior to presentation.  The day after vaccine administration, the patient experienced fatigue, shortness of breath, sore throat, and nausea, which was self-limiting and resolved quickly.  Three days after receiving the vaccine, the patient developed sharp and severe pain in the back of his left knee radiating down the back of his calf, with concomitant calf swelling. The pain increased upon exertion, prompting patient to present to the ED. He took no daily medications except for a multivitamin and denied any recent travel, trauma, illness, chest pain, shortness of breath, excessive alcohol or drug use, or family history of blood clots or miscarriages. No concomitant medications were reported.  Further workup of the deep venous thrombosis and extensive pulmonary emboli included hypercoagulable studies and workup of malignancy. Limited cancer screening, as outlined proved to be negative. Hypercoagulability studies were found to be negative, including heparin-induced thrombocytopenia (HIT) enzyme-linked immunosorbent assay (ELISA) and serotonin-release assay. Given the negative diagnostic workup for pertinent etiologies, the leading diagnosis established by the hematology consultants was vaccine-induced thrombosis without thrombocytopenia.  Authors concluded that this report did not confirm a causative link between the vaccine and thrombosis, but rather, authors suggested a plausible correlation due to the extensive and unprovoked nature of DVT/PE in this patient. Through this, authors aimed to shed light on a possible rare side effect of the Moderna COVID-19 vaccine to prompt awareness and future research studies.  Company comment: This literature non study case concerns a 31-year-old male patient with history of obesity grade I, no concomitant medications except for vitamins, no history of recent travel, trauma, illness, chest pain, excessive alcohol or drug use, or family history of blood clots reported, who experienced the unexpected, serious (Medically significant) AESI events of Pulmonary embolism, Deep vein thrombosis, Thrombosis (reported as Vaccine-induced thrombosis without thrombocytopenia) in context with second dose of mRNA-1273 vaccination. The day after vaccination patient had fatigue, shortness of breath, sore throat and nausea, which was self-limiting and resolved quickly. Three days later, he developed sharp and severe pain in the back of his left knee till calf, with concomitant calf swelling, pain worsened on exertion. Patient presented to the emergency, on examination, vitals were unremarkable, laboratory reports showed D-dimer of 5,335 ng/mL, a negative troponin, normal lactic acid level, and otherwise unremarkable cell counts, electrolytes, and platelets (147 × 10 9 /L). Electrocardiogram (EKG) showed a prolonged QT interval and inverted T waves. Although he had no tenderness upon palpation of the left knee, a Doppler ultrasound of the left lower extremities showed a thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins. Chest CT angiography (CTA) found extensive pulmonary emboli in the bilateral main pulmonary, lobar, and segmental arteries with possible mild right heart strain, later confirmed by an echocardiogram. Further workup of the deep venous thrombosis and extensive pulmonary emboli included hypercoagulable studies (including heparin-induced thrombocytopenia (HIT) enzyme-linked immunosorbent assay (ELISA) and serotonin-release assay), limited cancer screening, workup of Thrombophilia which were found negative. Based on the negative diagnostic workup for pertinent etiologies, patient was diagnosed with vaccine-induced thrombosis without thrombocytopenia. He was started on therapeutic anticoagulation, initially received enoxaparin 110 mg every 12 hours (Q12h), which was transitioned to apixaban 10 mg twice per day (BID) for seven days, followed by apixaban 5 mg daily for at least one year. Patient is advised regular follow up with hematologists for further anticoagulation. History of obesity grade I remains as risk factor for the events Pulmonary embolism, Deep vein thrombosis. Author concludes that this report does not confirm a causative link between the vaccine and thrombosis, but rather a plausible correlation was considered due to the extensive and unprovoked nature of DVT/PE. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.; Sender's Comments: This literature non study case concerns a 31-year-old male patient with history of obesity grade I, no concomitant medications except for vitamins, no history of recent travel, trauma, illness, chest pain, excessive alcohol or drug use, or family history of blood clots reported, who experienced the unexpected, serious (Medically significant) AESI events of Pulmonary embolism, Deep vein thrombosis, Thrombosis (reported as Vaccine-induced thrombosis without thrombocytopenia) in context with second dose of mRNA-1273 vaccination. The day after vaccination patient had fatigue, shortness of breath, sore throat and nausea, which was self-limiting and resolved quickly. Three days later, he developed sharp and severe pain in the back of his left knee till calf, with concomitant calf swelling, pain worsened on exertion. Patient presented to the emergency, on examination, vitals were unremarkable, laboratory reports showed D-dimer of 5,335 ng/mL, a negative troponin, normal lactic acid level, and otherwise unremarkable cell counts, electrolytes, and platelets (147 × 10 9 /L). Electrocardiogram (EKG) showed a prolonged QT interval and inverted T waves. Although he had no tenderness upon palpation of the left knee, a Doppler ultrasound of the left lower extremities showed a thrombus in the common femoral, superior, mid-, and distal femoral, popliteal, and likely posterior tibial veins. Chest CT angiography (CTA) found extensive pulmonary emboli in the bilateral main pulmonary, lobar, and segmental arteries with possible mild right heart strain, later confirmed by an echocardiogram. Further workup of the deep venous thrombosis and extensive pulmonary emboli included hypercoagulable studies (including heparin-induced thrombocytopenia (HIT) enzyme-linked immunosorbent assay (ELISA) and serotonin-release assay), limited cancer screening, workup of Thrombophilia which were found negative. Based on the negative diagnostic workup for pertinent etiologies, patient was diagnosed with vaccine-induced thrombosis without thrombocytopenia. He was started on therapeutic anticoagulation, initially received enoxaparin 110 mg every 12 hours (Q12h), which was transitioned to apixaban 10 mg twice per day (BID) for seven days, followed by apixaban 5 mg daily for at least one year. Patient is advised regular follow up with hematologists for further anticoagulation. History of obesity grade I remains as risk factor for the events Pulmonary embolism, Deep vein thrombosis. Author concludes that this report does not confirm a causative link between the vaccine and thrombosis, but rather a plausible correlation was considered due to the extensive and unprovoked nature of DVT/PE. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.