Microscopic Colitis/Lymphocytic Colitis; liquid stools; abdominal pain; nausea; chills; myalgia; fecal incontinence; This case has been considered invalid as Reporter with No First-hand knowledge. Upon receipt of follow-up information on (27Dec2022), this case now contains all required information to be considered valid.  This is a literature report from medical information team for the following literature source(s).   A 69-year-old female patient received BNT162b2 (BNT162B2), as dose 2, single (Batch/Lot number: unknown) for covid-19 immunisation. The patient's relevant medical history included: "gastroesophageal reflux" (unspecified if ongoing); "hyperlipidemia" (unspecified if ongoing); "paroxysmal supraventricular tachycardia" (unspecified if ongoing); "hypertension" (unspecified if ongoing). The patient's concomitant medications were not reported. Vaccination history included: Bnt162b2 (DOSE 1 single, without event), for COVID-19 immunization; Shingrix (previous administration of the second dose of the recombinant zoster vaccine (Shingrix) led to diffuse myalgias and joint pain for 2 weeks), for Immunization, reaction(s): "joint pain", "myalgias".  The following information was reported: COLITIS MICROSCOPIC (medically significant), outcome "not recovered", described as "Microscopic Colitis/Lymphocytic Colitis"; DIARRHOEA (non-serious), outcome "recovered", described as "liquid stools"; ABDOMINAL PAIN (non-serious), outcome "not recovered"; NAUSEA (non-serious), outcome "not recovered"; CHILLS (non-serious), outcome "not recovered"; MYALGIA (non-serious), outcome "not recovered"; ANAL INCONTINENCE (non-serious), outcome "not recovered", described as "fecal incontinence". The patient underwent the following laboratory tests and procedures: Colonoscopy: patchy erythema in the descending colon and rectos, notes: patchy erythema in the descending colon and rectosigmoid; C-reactive protein: negative; Full blood count: negative; Metabolic function test: negative; Oesophagogastroduodenoscopy: patchy erythema in the descending colon and rectos, notes: patchy erythema in the descending colon and rectosigmoid; Pathology test: changes consistent with LC, notes: Pathologic evaluation of mucosal biopsies revealed changes consistent with LC; Polymerase chain reaction: negative; SARS-CoV-2 test: negative; Serology test: negative. Therapeutic measures were taken as a result of colitis microscopic, diarrhoea, abdominal pain, nausea, chills, myalgia, anal incontinence.  Clinical course: Transient Lymphocytic Colitis After SARS-CoV2 mRNA Vaccine. This is the first scientific report describing lymphocytic colitis after administration of the Pfizer severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) messenger RNA (mRNA) vaccine. The patient developed liquid stools, abdominal pain, and nausea within 24 hours of receiving the second dose. Symptoms were persistent for 3 months but improved 113 days after onset. Laboratory profiles and gastrointestinal polymerase chain reaction were normal. Esophagogastroduodenoscopy and colonoscopy performed 98 days after onset revealed patchy erythema in the descending colon and rectosigmoid. Mucosal evaluation revealed lymphocytic colitis. Review of the Vaccine Adverse Event Reporting System revealed 5 cases of microscopic colitis after the second mRNA dose. This report and Vaccine Adverse Event Reporting System cases suggest providers should consider microscopic colitis in the differential diagnosis of patients with severe, persistent diarrhea after the SARS-CoV2 mRNA vaccine. Severe acute respiratory syndrome coronavirus 2 (SARSCoV2) has led to a global pandemic (1). Multiple vaccines have been developed and distributed worldwide to reduce the spread of the virus and mitigate disease severity. Of particular interest are messenger RNA (mRNA) vaccines, which offer improved protection from SARS-CoV2 compared with traditional vaccines (2). mRNA vaccines produced by Pfizer- BioNTech (Pfizer) and Moderna can cause various minor adverse events (AEs) after the first and/or second doses. Short-term side effects include pain/irritation at the injection site, chills, fever, and fatigue (3,4). Transient, typically mild gastrointestinal (GI) AEs including nausea and diarrhea have been reported as well. Recently, severe and longer-lasting side effects after vaccination have also been described (57). We report a case of lymphocytic colitis (LC) after the second dose of the Pfizer mRNA vaccine.   However, within 24 hours of her second dose, she suffered the onset of diarrhea, described as 23 loose to liquid stools (Bristol Stool Form [BSF] 6) per day (8). Before vaccination, the patient reported no significant GI issues and a normal bowel pattern with 12 formed stools per day (BSF 34). Over the next week, her symptoms remained stable, with occasional periods of chills and myalgia. On day 9 after onset, symptoms intensified to 35 watery stools per day (BSF 7), episodes of fecal incontinence, severe abdominal pain, nausea, and myalgia for a 36-hour period. After consultation with her primary care provider, ondansetron and loperamide were attempted with minimal benefit. Two months later when symptoms persisted, a GI consultation was obtained during which the patient reported continued watery diarrhea with mild to moderate abdominal pain and nausea. The patient reported no family history of irritable bowel syndrome, inflammatory bowel disease, or celiac disease. She denied a history of cholecystectomy or the recent start of new medications other than those prescribed for this illness. She had been taking aspirin 81 mg daily for over 10 years. She reported that previous administration of the second dose of the recombinant zoster vaccine (Shingrix) led to diffuse myalgias and joint pain for 2 weeks. Complete blood count, comprehensive metabolic profile, C reactive protein, and celiac serologies were negative. Initial and repeat , for pathogens were negative. An esophagogastroduodenoscopy and colonoscopy were performed on day 98 after onset, which revealed patchy erythema in the descending colon and rectosigmoid. The remainder of the colon and terminal ileum seemed normal. Pathologic evaluation of mucosal biopsies revealed changes consistent with LC.A previous esophagogastroduodenoscopy and colonoscopy performed in 2012 was unremarkable, acknowledging that no colon biopsies were obtained at that time. At follow-up 113 days after onset, the patient reported that abdominal symptoms were continuing to slowly improve and that her diarrhea had almost completely resolved.; Sender's Comments: Based on the available information in the case, an association between the reported events and The suspected drug cannot be ruled out.  The impact of this report on the benefit/risk profile of the Pfizer product 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.