Acute Severe Colitis after mRNA Coronavirus Disease 2019 Vaccination.

A 74-year-old woman developed acute severe colitis after receiving her sixth mRNA vaccine against coronavirus disease 2019 (COVID-19). On the day after vaccination, she experienced bloody diarrhea, abdominal pain, and high-grade fever. Laboratory tests revealed leukocytosis and increased C-reactive protein. Contrast-enhanced computed tomography revealed bowel wall thickening with a reduced contrast effect within the colon, in addition to ascites. Sigmoidoscopy revealed extensive sloughing of the mucosa. Her symptoms and laboratory findings improved immediately after the initiation of prednisolone therapy. Pre-discharge total colonoscopy revealed mucosal repair in most of the colon. Clinicians should acknowledge that severe acute colitis can occur after COVID-19 vaccination.