Clot in my leg/left leg; This spontaneous case was reported by a patient and describes the occurrence of THROMBOSIS (Clot in my leg/left leg) in a 73-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 057M21A, 027FZ1A, 011A21A and 030220A) for COVID-19 vaccination.     Concurrent medical conditions included Fish allergy (Salmon).   On 28-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 25-Feb-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 03-Sep-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 09-May-2022, received fourth dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 15-May-2022, after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced THROMBOSIS (Clot in my leg/left leg) (seriousness criterion medically significant). The patient was treated with APIXABAN (ELIQUIS) on 18-May-2022 at an unspecified dose and frequency. At the time of the report, THROMBOSIS (Clot in my leg/left leg) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 16-May-2022, Ultrasound testes: had a clot (abnormal) Had a clot.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   On 03-Sep-2021, received 1st booster of mRNA-1273 (Moderna COVID-19 Vaccine).  On 09-May-2022, received 2nd booster of mRNA-1273 (Moderna COVID-19 Vaccine).  Concomitant product use was not provided by the reporter.  The patient states that the medicine was supposed to provide relief to the pain. Her doctor said she was unfortunate to have a cosmetic reaction.  The symptoms got worse, but then patient took medicine.  The patient had to take Eliquis for 6 months to a year.  CC: This spontaneous case concerns an 73-year-old female patient, with no relevant medical history reported, who experienced the unexpected, serious (medically significant) Adverse Event of Special Interest of Thrombosis (reported as Clot in my leg/left leg), that occurred 6 days after the fourth dose of mRNA-1273 vaccine administration. Patient experienced a clot in her left leg. She underwent an ultrasound, which showed that she had a clot. The bulging vein in the leg still persists and is painful to touch. Patient was prescribed with Eliquis for 6 months to a year. Outcome of the event was reported as not resolved. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.; Sender's Comments: This spontaneous case concerns an 73-year-old female patient, with no relevant medical history reported, who experienced the unexpected, serious (medically significant) Adverse Event of Special Interest of Thrombosis (reported as Clot in my leg/left leg), that occurred 6 days after the fourth dose of mRNA-1273 vaccine administration. Patient experienced a clot in her left leg. She underwent an ultrasound, which showed that she had a clot. The bulging vein in the leg still persists and is painful to touch. Patient was prescribed with Eliquis for 6 months to a year. Outcome of the event was reported as not resolved. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.