3 blood clots behind my left knee; I am having a reaction; catch in my left knee/ it continued to hurt and throb; noticed my left foot was red and tender to the touch; noticed my left foot was red and tender to the touch / my leg and ankle are still so tinder.; I had broken out hives; they hurt and good gosh they itch; ontinued to hurt and throb; I had lost 25%of my strength; have a few and some scars; I haven't been able to where my shoes over 3 month I've been out of work for 3 months.; Around day 50 I woke up crying again; I was a bit tired; This spontaneous case was reported by a consumer and describes the occurrence of THROMBOSIS (3 blood clots behind my left knee) in a 51-year-old patient of an unknown gender who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included COPD.    On 15-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On an unknown date, the patient experienced THROMBOSIS (3 blood clots behind my left knee) (seriousness criterion medically significant), VACCINATION COMPLICATION (I am having a reaction), JOINT LOCK (catch in my left knee/ it continued to hurt and throb), ERYTHEMA (noticed my left foot was red and tender to the touch), TENDERNESS (noticed my left foot was red and tender to the touch / my leg and ankle are still so tinder.), URTICARIA (I had broken out hives), PRURITUS (they hurt and good gosh they itch), PAIN (ontinued to hurt and throb), ASTHENIA (I had lost 25%of my strength), SCAR (have a few and some scars), LOSS OF PERSONAL INDEPENDENCE IN DAILY ACTIVITIES (I haven't been able to where my shoes over 3 month I've been out of work for 3 months.), CRYING (Around day 50 I woke up crying again) and FATIGUE (I was a bit tired). At the time of the report, THROMBOSIS (3 blood clots behind my left knee), VACCINATION COMPLICATION (I am having a reaction), JOINT LOCK (catch in my left knee/ it continued to hurt and throb), ERYTHEMA (noticed my left foot was red and tender to the touch), PRURITUS (they hurt and good gosh they itch), PAIN (ontinued to hurt and throb), ASTHENIA (I had lost 25%of my strength), LOSS OF PERSONAL INDEPENDENCE IN DAILY ACTIVITIES (I haven't been able to where my shoes over 3 month I've been out of work for 3 months.), CRYING (Around day 50 I woke up crying again) and FATIGUE (I was a bit tired) outcome was unknown, TENDERNESS (noticed my left foot was red and tender to the touch / my leg and ankle are still so tinder.) and SCAR (have a few and some scars) had not resolved and URTICARIA (I had broken out hives) was resolving.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In 2021, Chest X-ray: normal (normal) clear. In 2021, Ultrasound scan: abnormal (abnormal) 3 blood clots behind left knee.     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) was unknown.       Concomitant medications were not reported.  The patient experienced catch in the left knee associated with pain, around the end of march/ first of April. She used a knee brace for a week She visited the ER (emergency room) clinic on an unspecified date. She was noticed to have a tender, red, left foot. Diagnostic tests revealed blood clots behind left knee. She was given a prescription for unspecified medications and asked to consult primary care physician.The patient reported that unspecified blood work was done every four days and she visited the doctor every week.She developed hives on an unspecified date. The doctor said it could have been because of stress or the medications.She reported that the swelling had eased but the leg and ankle were tender.  Treatment information was not provided.  Company Comment  Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.Further information has been requested   Most recent FOLLOW-UP information incorporated above includes: On 29-Jun-2021: Added medical history, added laboratory data, added date of vaccine administration, added events. The seriousness of case was updated to serious for the event of thrombosis.; Sender's Comments: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.Further information has been requested