TNF and inflammatory bowel disease: Thiopurines, including the use of azathioprine, mercaptopurine and thioguanine, are commonly used immunomodulators in IBD and have been variably associated with reduced vaccine responses (17, 19) For example, the CLARITY-IBD study demonstrated an association between immunomodulator use and lower seroconversion rates following both the first and second dose of vaccination, as well as reduced anti-SARS-CoV-2 antibody concentrations when patients used immunomodulators alongside TNF-α-antagonists (17, 25).