Booster:  profuse rectal bleeding; Booster: extreme, large amount of gas; Received her Pfizer COVID booster; Booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis; Booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis; Booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis; Booster: clouded in her head; This is a spontaneous report received from contactable reporter(s) (Other HCP). The reporter is the patient.  A 68 year-old female patient received bnt162b2 (BNT162B2), administration date 23Oct2021 (she knows it as in the afternoon, probably around 3:00 or 4:00PM ) (Lot number: FH8027) at the age of 68 years as dose 3 (booster), single for covid-19 immunisation. Relevant medical history included: "Osteopenia" (unspecified if ongoing), notes: diagnosed a number of years ago. She falls on the line for osteopenia so that is why she takes Vitamin D; "allergic to penicillin" (unspecified if ongoing); "allergic to antibiotic drug" (unspecified if ongoing). Concomitant medication(s) included: VITAMIN D [ERGOCALCIFEROL] taken for osteopenia; CALCIUM taken for osteopenia. She started no new medications in the 2 weeks leading up to the events reported. She took no other medications other than Vitamin D and a Centrum Multivitamin. Past drug history included: Allergic to tamiflu, reaction(s): "allergic to Tamiflu"; Allergy: z-pak, reaction(s): "Rash", notes: for 5 days, she just got a rash following these medications, it wasn't a severe reaction. Vaccination history included: Bnt162b2 (Second dose, Lot Number: EN6206), administration date: 24Mar2021, when the patient was 68 years old, for COVID-19 Immunization, reaction(s): "a little bit tired"; Bnt162b2 (first dose, Lot as EN6200, Anatomical Location:  she is thinking left arm but she can't be sure), administration date: 03Mar2021, when the patient was 68 years old, for COVID-19 Immunization, reaction(s): "With the first one, she had absolutely no reaction."; Flu shot (2-3 weeks prior to getting her booster dose.) for Immunization. The following information was reported: IMMUNISATION (medically significant) with onset 23Oct2021, outcome "unknown", described as "Received her Pfizer COVID booster"; COLITIS ULCERATIVE (medically significant), PROCTITIS (medically significant), COLITIS (medically significant) all with onset 2021, outcome "unknown" and all described as "Booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis"; RECTAL HAEMORRHAGE (medically significant) with onset 01Nov2021, outcome "unknown", described as "Booster:  profuse rectal bleeding"; HEAD DISCOMFORT (medically significant) with onset 2021, outcome "unknown", described as "Booster: clouded in her head"; FLATULENCE (medically significant) with onset 27Oct2021, outcome "unknown", described as "Booster: extreme, large amount of gas". The events "booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis", "booster:  profuse rectal bleeding", "booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis", "booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis", "booster: clouded in her head" and "booster: extreme, large amount of gas" were evaluated at the physician office visit. Events not require a visit to Emergency Room at this point. She mentions she is on a number of meds her doctor put her on.Clinical course as follows: she is a nurse but also the patient calling in regards to the Pfizer COVID Booster. The caller was informed by the GI specialist that she should call. She called her GI physician who she has had routine colonoscopies with before with no problems. Her GI doctor was able to do a flexible sigmoidoscopy to her descending colon where it was discovered she had diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis. Caller mentions she is reading off the paperwork received by her doctor. Her doctor did feel that the vaccine triggered an autoimmune response with inflammation. The doctors do feel its related and caused by the vaccine. The caller states she had no reaction to the first two vaccines. She clarifies the second one, she was just a little bit tired the second day. With the booster shot that she got, she felt very clouded in her head. The GI stuff started right away within 2 days. She knows the vaccine can affect the stomach and that is what she thought at first, but by day 4, it was profound. When probed for the seriousness criteria, she feels it is medically significant especially with COVID and her being on steroids. It's definitely a concern, she was healthy and now she is not. The patient underwent the following laboratory tests and procedures in 2021: biopsy: negative for cancers; body height: 5'1'' or 5'2''; colonoscopy: before with no problems; sigmoidoscopy: she had diffuse moderate to severe inflammation, notes: found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis. Therapeutic measures were taken as a result of colitis ulcerative, rectal haemorrhage, proctitis, colitis, head discomfort, flatulence included Prednisone 40mg x 2 weeks, 30mg daily x 1 week, 20mg daily x 1week, 10mg daily x 1 week; 5mg daily x 1 week, Balsalazide 750mg four tabs in AM and five tabs in PM, Mesalamine enemas 1 nightly. Since her doctor started her on prednisone, she is also now on Calcium 600mg twice a day because of the osteopenia. The caller again reads her doctor's impression: She has diffuse moderate inflammation found in rectum and sigmoid colon secondary to colitis to biopsies. She states the biopsies did come back negative for cancers. Reaction assessed: Booster: clouded in her head, Booster: profuse rectal bleeding, Booster: extreme, large amount of gas, Booster: diffuse moderate to severe inflammation found in her rectum and sigmoid colon, secondary to left-sided ulcerative colitis. Source of assessment: Primary Source Reporter, Method of assessment: Global Introspection: Drug result: Related.    No follow-up attempts are possible. No further information is expected.; Sender's Comments: Linked Report(s) : US-PFIZER INC-202101817582 Same patient/drug and different dose/AEs.