COVID-19 and COVID-19 Vaccinations Lead to Serological Responses in Patients with Inflammatory Bowel Diseases Independent of the Type of Immunomodulatory Medication

<b>Background/Objectives</b>: The COVID-19 pandemic and the development of vaccines provided the opportunity to monitor disease prevalence and outcomes, vaccinations, their side effects and serological responses in patients with inflammatory bowel disease (IBD). <b>Methods</b>: IBD patients of the outpatient clinic at the University Hospital Heidelberg who completed at least one questionnaire on COVID-19 and related vaccinations from July 2021 to August 2022 were included. Spike-IgG antibody titres were determined. Friedman tests, Wilcoxon signed-rank tests and Kruskal-Wallis tests were used for comparisons. The influence of IBD therapy was analysed using linear models with mixed effects. <b>Results:</b> The cohort included 520 patients (269 females, mean age = 45.3 years, 60.6% with Crohn's disease, 35.4% with ulcerative colitis, and 4.0% with unclassified IBD). Four hundred eighty patients (92.3%) received at least one COVID-19 vaccination, and 154 patients (29.6%) were infected by SARS-CoV-2. Among all of them, 94.4% achieved seroconversion. Triple-vaccinated patients with additional SARS-CoV-2 infection developed the highest serological responses (χ² = 16.51, <i>p</i> < 0.001, df = 3). An antibody decay over time was observed after the second (<i>p</i> < 0.001) and third vaccinations (<i>p</i> < 0.001). Regarding individual IBD medications, no differences in mean titres were found after two (χ² = 6.60, <i>p</i> = 0.36, df = 6) versus three vaccinations (χ² = 4.97, <i>p</i> = 0.42, df = 5). Linear models with mixed effects revealed no influence of IBD therapies on serological responses. <b>Conclusions</b>: The highest serological responses were observed in IBD patients after three vaccinations plus SARS-CoV-2 infection without significant differences between IBD therapies.