Biologic disease-modifying anti-rheumatic drugs (DMARDs) represent a potent treatment option for patients with immune-mediated inflammatory diseases. 1 Yet, infections make up the largest proportion of serious adverse events associated with biological DMARD therapy. 2 Throughout the COVID-19 pandemic, patients receiving immunosuppressive treatment were shown to be at higher risk of severe disease outcomes. 3 Vaccination could prevent these outcomes, but the efficacy of COVID-19 vaccines in these patients is incompletely understood. 4

Although studies investigating the effect of biological DMARDs on the development of immune responses to COVID-19 vaccines are slowly accumulating, most of our current knowledge relies on studies evaluating the serological responses to COVID-19 vaccines. 5 However, the serological response to COVID-19 vaccines is highly variable between individuals, in terms of both antibody titres and kinetics. 6, 7 There is also no cutoff value of antibody titres that clearly reflects protection from SARS-CoV-2 infection. 7