Extensive acute deep vein thrombosis (DVT) of the left lower extremity; Interchange of vaccine products; This literature-non-study case was reported in a literature article and describes the occurrence of DEEP VEIN THROMBOSIS (Extensive acute deep vein thrombosis (DVT) of the left lower extremity) in a 68-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.      Co-suspect product included non-company product COVID-19 VACCINE NRVV AD (CHADOX1 NCOV-19) (ASTRAZENECA COVID-19 VACCINE) for an unknown indication.    No Medical History information was reported.   On an unknown date, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form and first dose of COVID-19 VACCINE NRVV AD (CHADOX1 NCOV-19) (ASTRAZENECA COVID-19 VACCINE) (unknown route) 1 dosage form. On an unknown date, received second dose of COVID-19 VACCINE NRVV AD (CHADOX1 NCOV-19) (ASTRAZENECA COVID-19 VACCINE) (unknown route) dosage was changed to 1 dosage form. On an unknown date,  after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced DEEP VEIN THROMBOSIS (Extensive acute deep vein thrombosis (DVT) of the left lower extremity) (seriousness criterion medically significant) and INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products). The patient was treated with HEPARIN at an unspecified dose and frequency and RIVAROXABAN at an unspecified dose and frequency. At the time of the report, DEEP VEIN THROMBOSIS (Extensive acute deep vein thrombosis (DVT) of the left lower extremity) and INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products) outcome was unknown.      For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered DEEP VEIN THROMBOSIS (Extensive acute deep vein thrombosis (DVT) of the left lower extremity) and INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products) to be related.    Patient received booster dose of Moderna.  Concomitant medications were not reported.  Company comment: This literature-non-study case concerns a 68-year-old male patient with no medical history reported, who experienced the unexpected serious (medically significant) AESI of Deep vein thrombosis (reported as Extensive acute deep vein thrombosis (DVT) of the left lower extremity) approximately 2 weeks after the booster dose of mRNA-1273 vaccine. Patient received heparin and rivaroxaban as treatment. Patient received 2 doses of CHADOX1 NCOV-19 COVID 19 vaccine prior to the last dose (Interchange of vaccine products noted). The benefit-risk relationship of mRNA-1273 is not affected by this report.; Sender's Comments: This literature-non-study case concerns a 68-year-old male patient with no medical history reported, who experienced the unexpected serious (medically significant) AESI of Deep vein thrombosis (reported as Extensive acute deep vein thrombosis (DVT) of the left lower extremity) approximately 2 weeks after the booster dose of mRNA-1273 vaccine. Patient received heparin and rivaroxaban as treatment. Patient received 2 doses of CHADOX1 NCOV-19 COVID 19 vaccine prior to the last dose (Interchange of vaccine products noted). The benefit-risk relationship of mRNA-1273 is not affected by this report.