swelling has finally eased but my leg and ankle are still so tinder; The ultra sound found 3 blood clots behind my left knee; My left foot was red; My left foot was tender to the touch; I had lost 25%of my strength; I had broken out hives; They itch; They hurt; I still 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; Catch in my left/continued to hurt and throb / pain got so severe; I was a bit tired; This spontaneous case was reported by a consumer and describes the occurrence of THROMBOSIS (The ultra sound found 3 blood clots behind my left knee) in a 51-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included COPD.    On 15-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In March 2021, the patient experienced FATIGUE (I was a bit tired). On 01-Apr-2021, the patient experienced ARTHRALGIA (Catch in my left/continued to hurt and throb / pain got so severe). On an unknown date, the patient experienced THROMBOSIS (The ultra sound found 3 blood clots behind my left knee) (seriousness criterion medically significant), ERYTHEMA (My left foot was red), TENDERNESS (My left foot was tender to the touch), ASTHENIA (I had lost 25%of my strength), URTICARIA (I had broken out hives), PRURITUS (They itch), PAIN (They hurt), SCAR (I still 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) and PERIPHERAL SWELLING (swelling has finally eased but my leg and ankle are still so tinder). At the time of the report, THROMBOSIS (The ultra sound found 3 blood clots behind my left knee), ERYTHEMA (My left foot was red), TENDERNESS (My left foot was tender to the touch), ASTHENIA (I had lost 25%of my strength), URTICARIA (I had broken out hives), PRURITUS (They itch), PAIN (They hurt), SCAR (I still 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), PERIPHERAL SWELLING (swelling has finally eased but my leg and ankle are still so tinder), FATIGUE (I was a bit tired) and ARTHRALGIA (Catch in my left/continued to hurt and throb / pain got so severe) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In 2021, Chest X-ray: clear (normal) Normal. In 2021, Ultrasound scan: 3 blood clots behind left knee (abnormal) abnormal.     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown.       No relevant concomitant medications were provided.  Reportedly, around the end of Mar-2021 to 01-Apr-2021, the patient noticed a catch in her left knee. The patient then visited the emergency room  and had Chest-x Ray and ultra sound and she was told by the doctor that she had 3 blood clots behind her left knee. The patient was prescribed medicines (names not specified). The patient had hives around day 50 (after vaccine). At around day 118 (since the patient received the vaccine), she was still in need of help for wearing her socks. The patient could walk for almost 20 minutes with the walker. No other treatment information was provided.  Company Comment: Very limited information regarding this events has been provided at this time.   Most recent FOLLOW-UP information incorporated above includes: On 02-Jul-2021: Additional information received contained narrative information describing current health status.; Sender's Comments: Very limited information regarding this events has been provided at this time.