Kinetics of SARS-CoV-2-Spike (S1) specific IgG antibodies. Geometric mean concentrations (GMC) with 95% CI of A) S1-specific IgG against ancestral virus hu-1 in BAU/mL in IBD patients treated with either anti-TNFα (n = 19) or α4β7-integrin-antagonists (n = 17) and controls (n = 20) measured before the first and four weeks and six months after the second dose, as well as four weeks after booster dose of SARS-CoV-2 mRNA vaccine (BNT162b2 or mRNA-1273); dashed line - positive cut-off for S1-specific IgG at 35.2 BAU/mL; B) S1-specific IgG against Omicron BA.1 (in RU/mL), dashed line—positive cut-off for BA.1 S1-specific IgG at 11.0 RU/m; C) IgG specific for RBD of Omicron BA.4/5 (as OD) and D) inhibition capacity of BA.4/0.5-specific Abs (as % inhibition) measured six months after the second dose and four weeks after booster dose; OD values > 0.25 and inhibition levels of >20% were considered positive (black dashed line), inhibition levels >50% as relevant (red dashed line). Asterisks positioned below IBD/anti-TNF-α data points represent significance of difference to controls, below IBD/integrin antagonist datapoints difference between this group and controls. Asterisks with a band indicate significant changes over time; band in light red - difference between controls and IBD/anti-TNF-α, in dark red - difference between controls and IBD/integrin antagonist. Abbreviations: BAU, binding antibody units; mo, months; RBD, receptor-binding domain; RU, relative units; S1, SARS-CoV-2 Spike protein 1. ANOVA with linear contrasts; ∗∗∗∗p ≤ 0.0001; ∗∗p ≤ 0.01; ∗p ≤ 0.05.