COvid-19 Vaccines Booster in Immunocompromised Rheumatic Diseases (COVBIRD).

In the midst of a fourth wave and the circulation of the delta variant, Quebec and Ontario offer a third dose of mRNA COVID-19 vaccine to immunosuppressed patients including people living with systemic autoimmune rheumatic diseases (SARD). However, the safety and the response to a third dose of vaccine in rheumatic disease patients is unknown. Moreover, initial results from an ongoing study demonstrated that SARD patients treated with rituximab, a drug that depletes cells producing antibodies, have a poor response to two doses of an mRNA vaccine. Since this group is also less likely to respond to a third vaccine dose, defining strategies to enhance responses to COVID-19 vaccines in these vulnerable patients is a priority. Hypothesis: A fourth dose of a non-mRNA vaccine, in SARD patients treated with Rituximab who do not respond to a third dose, is safe and enhances the number of patients who develop post-vaccine antibody responses. Primary Aims: To evaluate the safety of a 4th dose of vaccine in SARD patients treated with rituximab and the vaccine induced antibody responses. Secondary Aims: To compare the response following a 4th dose of a non-mRNA vaccine; to evaluate the effect of immunosuppressive treatment on the response post-4th dose; to compare the rates of disease flares post-4th dose of a non-mRNA vaccine; to assess the persistence of humoral responses induced by a 4th dose of a non-mRNA vaccines. Design: This multicenter clinical trial will enroll SARD patients on rituximab who did not respond to a third dose of a COVID-19 vaccine. These patients will be offered a 4th dose of non-mRNA COVID-19 vaccines that will be approved in the coming months by Health Canada. Significance: This study is key to inform public health authorities on the advantage of using specific vaccine types to achieve satisfactory vaccination in the most vulnerable SARD patients.