Rituximab-treated rheumatic patients: B cells predict seroconversion after COVID-19 boost or revaccination in initial vaccine non-responders

Abstract Objectives To investigate the effect of either a booster vaccine (one dose) or revaccination (two doses 3 weeks apart) on the antibody response to the COVID-19 mRNA vaccines in patients with rheumatic disease (RD) treated with rituximab (RTX) who had not produced vaccine-reactive antibodies after the initial two vaccine doses. Further, to examine if B cell levels in peripheral blood predicted seroconversion. Methods We included 91 RTX-treated RD patients previously vaccinated against COVID-19. Patients were offered revaccination or a single booster vaccination with an mRNA vaccine. Serum total antibodies against SARS-CoV-2 spike protein were measured before and 6 weeks after the last vaccine dose. B cells (CD19+CD45+) were measured by flow cytometry at inclusion. Results Of RD patients with undetectable SARS-CoV-2 antibody levels before inclusion, seroconversion was seen in 38% 6 weeks after the booster dose and 32% after revaccination. Patients receiving revaccination had significantly higher antibody levels than patients receiving a booster dose (P