Background:
COVID-19 vaccine-induced antibody responses are reduced in patients with inflammatory bowel disease (IBD) taking anti-TNF or tofacitinib after two vaccine doses. We sought to determine whether immunosuppressive treatments were associated with reduced antibody and T cell responses after a third vaccine dose.

Methods:
352 adults (72 healthy controls and 280 IBD) were sampled 28-49 days after a third dose of SARS-CoV-2 vaccine. IBD medications studied included thiopurines (n=65), infliximab (n=46), thiopurine/infliximab combination therapy (n=49), ustekinumab (n=44), vedolizumab (n=50) or tofacitinib (n=26). SARS-CoV-2 spike antibody binding and T cell responses were measured.

Findings:
Geometric mean [geometric SD] anti-S1 RBD antibody concentrations increased in all groups following a third dose, but were significantly lower in patients treated with infliximab (2736.8 U/mL [4.3]; P<0.0001), infliximab and thiopurine combination (1818.3 U/mL [6.7]; P<0.0001) and tofacitinib (8071.5 U/mL [3.1]; P=0.0018) compared to controls (16774.2 U/ml [2.6]). There were no significant differences in anti-S1 RBD antibody concentrations between control subjects and thiopurine (12019.7 U/mL [2.2]; P=0.099), ustekinumab (11089.3 U/mL [2.8]; P=0.060), nor vedolizumab treated patients (13564.9 U/mL [2.4]; P=0.27). In multivariable modelling, lower anti-S1 RBD antibody concentrations were independently associated with infliximab (Geometric mean ratio 0.15, 95% CI 0.11-0.21, P<0.0001), tofacitinib (0.52, 95% CI 0.31-0.87, P=0.012) and thiopurine (0.69, 95% CI 0.51-0.95, P=0.021), but not with ustekinumab (0.64, 95% CI 0.39-1.06, P=0.083), or vedolizumab (0.84, 95% CI 0.54-1.30, P=0.43). Previous SARS-CoV-2 infection (1.58, 95% CI 1.22-2.05, P=0.00056) and older age (0.88, 95% CI 0.80-0.97, P=0.0073) were independently associated with higher and lower anti-S1 antibody concentrations respectively. Antigen specific T cell responses were similar in all groups, except for recipients of tofacitinib without evidence of previous infection, where T cell responses were significantly reduced relative to healthy controls (p=0.021).

Interpretation:
A third dose of COVID-19 vaccine induced a boost in antibody binding in immunosuppressed patients with IBD, but these responses were reduced in patients taking infliximab, infliximab/thiopurine combination and tofacitinib. Tofacitinib was also associated with reduced T cell responses. These findings support continued prioritisation of immunosuppressed groups for further booster dosing, particularly those on anti-TNF and Janus Kinase (JAK) inhibitors.

Funding:
Financial support was provided as a Research Grant by Pfizer Ltd.