Objective Flares of inflammatory bowel disease (IBD) can occur infrequently after vaccination for coronavirus disease 2019 (COVID-19), although the details of this phenomenon are poorly understood. To clarify the possibility of an unfavorable response in patients with IBD, we investigated IBD-related symptoms during the COVID-19 vaccination. Methods Between October 2021 and February 2022, we obtained the COVID-19 vaccination status of 411 IBD patients who were being treated at our institution. The disease course of IBD after vaccination was investigated in 188 patients with ulcerative colitis (UC) and 119 patients with Crohn’s disease (CD) who had received at least one dose of the vaccine during the clinical remission phase. The baseline characteristics before vaccination were compared between the patients with UC with or without disease flares. Results During the 30-day follow-up period, eight patients with UC (4.3%) and one patient with CD (0.8%) experienced disease flares following vaccination. Disease flares occurred after the first vaccination in six patients and after the second vaccination in three patients. As for the timing of onset of disease flares, eight events (88.9%) occurred within one week of vaccination. Two patients required hospitalization, and one patient with CD required surgery for an intra-abdominal abscess. The baseline characteristics did not significantly differ between patients with UC who experienced flares and those who did not. Conclusions IBD flares following COVID-19 vaccination are rare and vaccination should therefore be recommended for patients with IBD. However, the possibility of disease flares should be considered for approximately one week after each vaccination, especially in patients with UC.
