Immunogenic response leading to Rituximab-Associated Colitis; This literature-non-study case was reported in a literature article and describes the occurrence of COLITIS (Immunogenic response leading to Rituximab-Associated Colitis) in a 49-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.       The patient's past medical history included Splenectomy. Concurrent medical conditions included Follicular lymphoma stage IV (in remission on RTX maintenance therapy,). Concomitant products included RITUXIMAB for Follicular lymphoma stage IV.    On an unknown date, the patient received dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, the patient experienced COLITIS (Immunogenic response leading to Rituximab-Associated Colitis) (seriousness criterion medically significant). The patient was treated with BUDESONIDE (oral) for Colitis, at an unspecified dose and frequency; DICYCLOVERINE HYDROCHLORIDE (BENTYL) for Colitis, at an unspecified dose and frequency and LOPERAMIDE for Colitis, at an unspecified dose and frequency. At the time of the report, COLITIS (Immunogenic response leading to Rituximab-Associated Colitis) outcome was unknown. Possible    DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Biopsy: abnormal Biopsies revealed active chronic ileitis with eosinophils, occasional crypt abscess and crypt destruction. On an unknown date, Colonoscopy: abnormal Initial colonoscopy demonstrated diffuse scattered clean based ulcers between 1-8 mm in size throughout the colon and terminal ileum. and abnormal Repeat colonoscopy demonstrated circumferential hyperemia/edema with apthous ulcers throughout the colon.. On an unknown date, Computerised tomogram: abnormal CT imaging demonstrated diffuse colonic wall thickening with new interval adjacent pancolonic fat stranding.. On an unknown date, Cytomegalovirus test: negative (Negative) Negative. On an unknown date, Herpes simplex test: negative (Negative) Negative.     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown.   For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered COLITIS (Immunogenic response leading to Rituximab-Associated Colitis) to be related.    Patient presented with 6 wks of watery, non-bloody diarrhea, right upper quadrant pain, >10 lb weight loss and fever.  Infectious work up was negative. Negative for signs of recurrent lymphoma. They planned  to treat as a Crohn's patient with corticosteroid induction and trial Vedolizumab for maintenance of remission.  CC: This case concerns a 49-y/o male subject w/ a medical history of stage IVa follicular lymphoma in remission on RTX maintenance therapy and splenectomy, who experienced the serious unexpected event of Colitis (Immunogenic response leading to Rituximab-Asstd Colitis). The event occurred 2 days after a dose of mRNA 1273, dose no. unknown. Patient presented with presented with 6 wks of watery, non-bloody diarrhea, right upper quadrant pain, >10 lb weight loss and fever. Infectious work up was negative and CT scan showed diffuse colonic wall thickening w/ new interval adjacent pancolonic fat stranding. Initial colonoscopy showed diffuse scattered clean based ulcers between 1-8 mm in size throughout the colon and terminal ileum. Biopsies revealed active chronic ileitis w/ eosinophils, occasional crypt abscess and crypt destruction negative for HSV, CMV or signs of recurrent lymphoma. He was then treated with oral budesonide, bentyl and loperamide but returned 6 wks later w/o any relief in abdominal pain or diarrhea. Repeat colonoscopy demonstrated circumferential hyperemia/edema with apthous ulcers throughout the colon.  At the time of the report, outcome of the event was Unknown. Rechallenge is Not applicable as there is no information regarding dose number is given. The patient's medical hx of stage IVa follicular lymphoma in remission on RTX maintenance therapy and splenectomy remain as confounders. The reporter believes there may be a correlation between the immunogenicity of mRNA vaccines like mRNA-1273 and the induction of colitis in patients while on immunosuppressants The benefit-risk relationship of mRNA 1273 is not affected by this report.   Reporter did not allow further contact   Most recent FOLLOW-UP information incorporated above includes: On 02-Dec-2021: Follow up received by safety 03-Dec-2021 included an Email; Sender's Comments: This case concerns a 49-year old, male subject with a medical history of stage IVa follicular lymphoma in remission on RTX maintenance therapy and splenectomy, who experienced the serious unexpected event of Colitis (Immunogenic response leading to Rituximab-Associated Colitis). The event occurred 2 days after a dose of mRNA 1273 VACCINE, dose number unknown. Patient presented with presented with 6 weeks of watery, non-bloody diarrhea, right upper quadrant pain, >10 pound weight loss and fever. Infectious work up was negative and CT imaging demonstrated diffuse colonic wall thickening with new interval adjacent pancolonic fat stranding. Initial colonoscopy demonstrated diffuse scattered clean based ulcers between 1-8 mm in size throughout the colon and terminal ileum. Biopsies revealed active chronic ileitis with eosinophils, occasional crypt abscess and crypt destruction negative for HSV, CMV or signs of recurrent lymphoma. He was then treated with oral budesonide, bentyl and loperamide but returned 6 weeks later without any relief in abdominal pain or diarrhea. Repeat colonoscopy demonstrated circumferential hyperemia/edema with apthous ulcers throughout the colon.  At the time of the report, outcome of the event was Unknown. Rechallenge is Not applicable as there is no information regarding dose number is given. The patient's medical history of stage IVa follicular lymphoma in remission on RTX maintenance therapy and splenectomy remain as confounders. The reporter believes there may be a correlation between the immunogenicity of mRNA vaccines like mRNA-1273 and the induction of colitis in patients while on immunosuppressants The benefit-risk relationship of mRNA 1273 is not affected by this report.