Sonogram shows extensive clots throughout superficial greater saphenous veins; Severe lower leg pain; Received third dose of the Covid 19 Vaccine; Received third dose of the Covid 19 Vaccine; This is a spontaneous report received from a contactable physician (patient). A 68-year-old male patient received third dose of bnt162b2 (PFIZER-BIONTECH COVID-19 mRNA VACCINE, solution for injection, Lot number: EW0198) via an unspecified route of administration on 20Aug2021 (at the age of 68-year-old) as dose 3, single for COVID-19 immunisation. Patient do not have any medical history including any illness at time of vaccination and There were no concomitant medications. Patient do not have any relevant family medical history. Patient did not receive any other vaccines prior to vaccination (within 4 weeks) and patient was healthy prior to vaccination. Patient previously received first dose of bnt162b2 (PFIZER-BIONTECH COVID-19 mRNA VACCINE, solution for injection, Lot number: EL1284) via an unspecified route of administration on 22Dec2020 (at the age of 67-year-old) as dose 1, single and then dose 2 (Lot number: EL1283) via an unspecified route of administration on 14Jan2021 for COVID-19 immunisation. It was reported that caller states he was calling about the Pfizer Product: Covid 19 Vaccine. States he was calling about a suspected, and highly likely, side effect. States he had the third vaccine about a week ago. One week later he had severe lower leg pain He thought it was musculoskeletal, so he treated it as such. States it did not go away. States he had a sonogram done that shows extensive clots throughout the superficial greater saphenous veins. Caller states his leg pain has been pretty bad the entire time that he has had it. States that hopefully it doesn't move deeper into his system and become life threatening. States he had the sonogram, doppler ultrasound, today. He has to start Eliquis today also and will be on it for a minimum of three months. The patient experienced severe lower leg pain on 27Aug2021, sonogram shows extensive clots throughout superficial greater saphenous veins on 03Sep2021 received third dose of the covid 19 vaccine on 20Aug2021. The patient underwent lab tests and procedures which included ultrasound doppler: extensive clots on 03Sep2021 More information available: No, ultrasound scan: extensive clots on 03Sep2021 More information available: No. He called his primary care provider and told him his symptoms. His primary care ordered him the sonogram. Then caller states he called his cardiologist to discuss treatment. Patient did not visit the emergency room or physician office for the events. Outcome of events severe lower leg pain was not recovered and sonogram shows extensive clots throughout superficial greater saphenous veins was unknown.; Sender's Comments: Based on the information available in the case , a contributory role of the suspect product bnt162b2 to the reported events cannot be excluded. Case will be reassessed upon receipt of additional information.  The impact of this report on the benefit/risk profile of the Pfizer drug is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to Regulatory Authorities, Ethics Committees, and Investigators, as appropriate