blood clot; Right leg swelled and achy; Right leg swelled and achy; This is a spontaneous report from a contactable nurse (patient). A 67-year-old female patient received BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE, Batch/Lot Number: EP7534),dose 1 via an unspecified route of administration, administered in Arm Left on 16Mar2021 (at the age of 67years) as single dose for Covid-19 immunization. Medical history included ongoing Beta thalassemias. The patient's concomitant medications were not reported. The patient did not receive any other vaccines within 4 weeks prior to the COVID vaccine. The patient stated she has never had a problem with vaccinations, and she gets the flu vaccine every year. The patient reported that after the first injection coincidentally she did develop a blood clot in her lower leg. She thinks that it was due to a plane ride, but she has never had a blood clot before the injection. She added that she had the first dose on 16Mar2021 and developed a clot in a week. She further clarified that she got her first injection on 16Mar2021 and realized when she went on a flight, which is not that far she developed that clot and was having problems shortly after flight home on 24Mar2021 where her leg swelled up and she is on blood thinners since she went to the emergency room. She added that she developed the clot sometime between that flight and 02Apr2021. She had a doppler study on an unspecified date and it showed a blood clot.  She stated that the outcome was she does not have the blood clot (as reported) but she will be on blood thinners and she needs to follow up on her scan to see if the clot issue is resolved but she will not have a doppler scan for another month or two and the blood thinner she is taking is Xarelto. She also stated that her right leg swelled up and it felt like a log. She reported it felt achy and swollen quite a bit from knee down and her leg was achy. It started between 24Mar2021 and by time she went to the emergency room she was not getting better. She had her symptoms for a week and toward the end of the week she thought she had a blood clot since it was not getting better it just got worse. She added that right now it is not swollen but she has been supine, and she does believe that it is better. The outcome of events was recovering. (As reported "outcome is unknown but pretty sure it has improved because of the blood thinners"./She stated she does not think it has resolved because it takes time for clots to resolve./She added that right now it is not swollen but she has been supine, and she does believe that it is better.)  The reporter stated for the seriousness criteria for event blood clot: she believes as a nurse that any blood clot is extremely dangerous, and she was not hospitalized but obviously a blood clot is serious, and she could have ended up with pulmonary embolism. The seriousness for events right leg swelled and achy was reported as medically disabling.  Causality assessment: Patient stated for the blood clot she has doubts if it was related to the vaccine but is it something that should be known about; for the leg swelling and achy she has doubts but it could have been the plane ride.; Sender's Comments: Based on the current available information, the reported events are most likely related to an intercurrent or underlying condition which is unlikely related to the suspected drug. The plane ride may provide an explanation for the events.  The case will be reassessed if additional information becomes available.