Diagnosed with May-thurner syndrome; Deep vein thrombosis; Both of her feet were only slightly swollen; Dull minor headache; Off-label use; Inappropriate schedule of vaccine administered; Localized discomfort where injection of second dose of Pfizer COVID-19 Vaccine was given; This is a spontaneous report from a contactable consumer (patient).   A 65-year-old female patient (weight: 77.56 kg, height: 157 cm) received the second dose of BNT162B2 (Pfizer-Biontech Covid-19 Vaccine) at single dose, in the upper left arm, on 23Jan2021, for COVID-19 immunisation. Relevant medical history included thyroid condition from an unspecified date (over 25-30 years before this report) and ongoing, controlled with levothyroxine sodium (SYNTHROID); and breast cancer from an unspecified date, in 2019 (treatment and surgery on an unspecified date, in 2019. Presumed resolved with radiation treatment, but no treatment within a year prior to getting Pfizer COVID-19 vaccine). The patient previously, on 05Jan2021 (18 days before the second dose), received the first dose of BNT162B2 (Pfizer-Biontech Covid-19 Vaccine) for COVID-19 immunisation. After the first dose, the patient experienced localized discomfort at the injection site and swelling of feet. Concomitant medication included levothyroxine sodium (SYNTHROID) from an unspecified date and ongoing, 0.88 mg, daily, for thyroid condition. On 23Jan2021, the patient experienced injection site discomfort described as "localized discomfort where injection of second dose of Pfizer COVID-19 Vaccine was given". On 24Jan2021, she had dull minor headache. On an unspecified date, the patient was hospitalized after the second dose and was diagnosed with May-thurner syndrome. She clarified that May-Thurner syndrome was where the iliac artery collapses and crushed the iliac vein in the upper abdomen; from that point down it started creating a blood clot. She developed a deep vein thrombosis (DVT) from her left ankle up to her right rib cage area; it was a monster. On 10Feb2021, the patient experienced deep vein thrombosis and thrombectomy was performed on the same day (outpatient thrombectomy surgery, performed 10Feb2021. It was a great surgery, very corrective. She never did have any pain or discomfort which confused everyone. She felt fine this whole time, no issues). On an unspecified date, both of her feet were only slightly swollen. Relevant laboratory test, performed on an unspecified date, in 2021, included computerised tomogram (CT scan with contrast of her abdomen and chest) that showed deep vein thrombosis: left ankle-right ribcage area. The adverse events May-Thurner syndrome and deep vein thrombosis were assessed as serious, hospitalization required from 02Feb2021 to 10Feb2021. The patient recovered from deep vein thrombosis on 10Feb2021, recovered from headache on 26Jan2021, recovered from swelling of feet and vaccination site discomfort on an unspecified date, while clinical outcome of the other events was unknown. Her vascular surgeon said he did not believe these events were vaccine related but cannot rule it out; her Primary Care Physician absolutely believed the events were vaccine related.   The information on the lot number has been requested.