Combination therapy of infliximab and thiopurines, but not monotherapy with infliximab or vedolizumab, is associated with attenuated IgA and neutralisation responses to SARS-CoV-2 in inflammatory bowel disease.

There is substantial interest regarding the perceived risk that immunomodulator and biologic therapy could have on COVID-19 disease severity among patients with inflammatory bowel disease (IBD) and clinicians. In this study, we show that infliximab/thiopurine combination therapy is associated with significantly lower IgA, a range of lower IgG responses as well as impaired neutralising antibody responses, compared to responses observed in healthy individuals. We also demonstrate that whilst IgG responses were significantly reduced in individuals with IBD treated with infliximab or vedolizumab monotherapy compared to healthy controls, there was no significant reduction in IgA and neutralising antibody responses. As neutralising antibody responses correlate with protection, this observation may provide the mechanistic explanation for the observation reported by the SECURE-IBD study that individuals on infliximab/thiopurine combination therapy were at greater risk of severe COVID-19 outcomes than patients on monotherapy.