blood clots in her legs and lungs; blood clots in her legs and lungs; back and legs were hurting; couldn't walk.; back and legs were hurting; alertness declining; activity declining; This spontaneous case was reported by a consumer (subsequently medically confirmed) and describes the occurrence of THROMBOSIS (blood clots in her legs and lungs), PULMONARY EMBOLISM (blood clots in her legs and lungs), BACK PAIN (back and legs were hurting), GAIT DISTURBANCE (couldn't walk.), PAIN IN EXTREMITY (back and legs were hurting), DEPRESSED LEVEL OF CONSCIOUSNESS (alertness declining) and DECREASED ACTIVITY (activity declining) in a 20-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. Unknown) for COVID-19 vaccination.     No medical history was reported.    On 22-Feb-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 18-Mar-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to .5 milliliter. On 27-May-2021, the patient experienced DEPRESSED LEVEL OF CONSCIOUSNESS (alertness declining) (seriousness criteria hospitalization, disability and medically significant) and DECREASED ACTIVITY (activity declining) (seriousness criteria hospitalization and disability). On an unknown date, the patient experienced THROMBOSIS (blood clots in her legs and lungs) (seriousness criteria hospitalization, disability and medically significant), PULMONARY EMBOLISM (blood clots in her legs and lungs) (seriousness criteria hospitalization, disability and medically significant), BACK PAIN (back and legs were hurting) (seriousness criteria hospitalization and disability), GAIT DISTURBANCE (couldn't walk.) (seriousness criteria hospitalization and disability) and PAIN IN EXTREMITY (back and legs were hurting) (seriousness criteria hospitalization and disability). The patient was hospitalized on 16-May-2021 due to BACK PAIN, GAIT DISTURBANCE, PAIN IN EXTREMITY, PULMONARY EMBOLISM and THROMBOSIS. The patient was treated with HEPARIN for Coagulopathy, at a dose of 1 dosage form; Surgery (thrombectomy and Intubated) for Thrombosis and Surgery (thrombectomy and Intubated) for Pulmonary embolism. At the time of the report, THROMBOSIS (blood clots in her legs and lungs), PULMONARY EMBOLISM (blood clots in her legs and lungs), BACK PAIN (back and legs were hurting), GAIT DISTURBANCE (couldn't walk.), PAIN IN EXTREMITY (back and legs were hurting), DEPRESSED LEVEL OF CONSCIOUSNESS (alertness declining) and DECREASED ACTIVITY (activity declining) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In May 2021, Blood creatinine: 5.37 (High) high. In May 2021, Blood potassium: high (High) high. In May 2021, Glomerular filtration rate: 9.5 (Low) low. In May 2021, Imaging procedure: abnormal (abnormal) had new imaging and she was still developing clots. In May 2021, Ultrasound abdomen: inconclusive (Inconclusive) inconclusive.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   She was in the cardiac intensive care unit (ICU). She had a thrombectomy and was on heparin. They intubated her and put her on the ECMO machine on 19 May 2021. The patient got off ECMO on 24 May 2021 and the intubation tube was removed 25 May 2021. They were having trouble obtaining a non-hemolyzed sample from her since 27 May 2021.  The patients concomitant medication information included birth control pills.  Very limited information regarding these events have been provided at this time. However subject's use of birth control pills can be a confounding factor to the events thrombosis and Pulmonary embolism. No further information is expected.; Sender's Comments: Very limited information regarding these events have been provided at this time. However subject's use of birth control pills can be a confounding factor to the events thrombosis and Pulmonary embolism. No further information is expected.