booster; diarrhea; This is a spontaneous report received from contactable reporter(s) (Consumer or other non HCP) from medical information team. The reporter is the patient.  A 82 year-old female patient received bnt162b2 (BNT162B2), administered in arm left, administration date 06Oct2021 (Lot number: 30155BA) at the age of 82 years as dose 3 (booster), single for covid-19 immunisation. Relevant medical history included: "diarrhea" (unspecified if ongoing). Concomitant medication(s) included: COUMADIN; PEPTO BISMOL [BISMUTH SUBSALICYLATE;CALCIUM CARBONATE]. Vaccination history included: Bnt162b2 (Dose-1, Lot Number: EL9261, Anatomical Location: left arm ), administration date: 20Jan2021, when the patient was 82 years old, for COVID-19 immunization; Bnt162b2 (Dose-2, Lot Number: EN6201, Anatomical Location: right arm ), administration date: 10Feb2021, when the patient was 82 years old, for COVID-19 immunization. The following information was reported: IMMUNISATION (non-serious) with onset 06Oct2021, outcome "unknown", described as "booster"; DIARRHOEA (non-serious) with onset Oct2021, outcome "not recovered", described as "diarrhea". Therapeutic measures were taken as a result of diarrhoea.  Additional information: The patient had diarrhea since the ending of Oct2021, she had a bad episode again last night and it's watery. She was home-bound because of this, she needs to stay close to the bathroom. She's taking Imodium and Pepto-Bismol and it will slow it down but when she goes off of the medication the diarrhea comes back and gets real watersy and forceful. Patient experienced first two bouts of diarrhea were so bad that she was throwing up From: Oct2021 To Oct2021). She was having symptoms after her booster shot which she had in the middle of Oct2021. She had severe diarrhea and its still ongoing. She had been talking to her doctor off and on and she is not being much help. The doctor this morning said to take Metamucil and her Imodium. She would take antidiarrheal medication and it would settle it down and then she would have another rebound and twice she threw up with it. That began shortly after the booster, about a week after the booster shot she inquired for outcome of the diarrhea and she states that she would say its not as bad as the first two bouts were that she had where she did the throwing up. She had been watching what she eats and is trying to drink the electrolytes to keep her energy up, because that takes a lot out of a person, and then she will go 3 to 4 days and she is fine and then it'll start up again. She said say that sometimes she can go about a week between bouts and usually that's when she was taking the Pepto-Bismol for it. But then she realizes that she was not supposed to keep on that medication so she will go off of it, the Pepto-Bismol, and then her diarrhea was back with full force and really watery. The only medication that she was taking Coumadin and she has been on that for years. The adverse events did not require a visit to emergency room and physician office. She had her flu shot between her 2nd dose of the Pfizer COVID vaccine and her booster dose of the Pfizer COVID vaccine, but she doesn't remember the exact day. She thinks that it was maybe 2 weeks before her booster dose. Her doctor was filling out a prescription for her at this time and it was for an antidiarrheal medication but the doctor didn't say what type it was but said that it would be a prescription.   Follow-up attempts are completed. No further information is expected.