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Introduction: Systemic lupus erythematosus (SLE) patients exhibit B-cell abnormalities. Although there are concerns about reduced antibody responses to SARS-CoV-2 vaccines, detailed data on B-cell-specific responses in SLE remain scarce. Understanding the responsiveness to novel vaccine antigens, and boosters number, is important to avoid unnecessarily prolonged isolation of immunocompromised individuals. We assessed humoral and antigen-specific B-cell subset responses, including changes in isotype switching, prior to and after several doses of SARS-CoV-2 vaccines., Methods: Blood samples were obtained prior to and after SARS-CoV-2 vaccination from cross-sectional and longitudinal cohorts of previously uninfected patients with SLE (n = 93). Healthy participants receiving SARS-CoV-2 vaccines were recruited as controls (n = 135). We measured serum antibody titres, their neutralizing capacity, and vaccine-specific memory B-cell subsets., Results: Impaired IgG, IgA, and neutralizing responses against the original and various SARS-CoV-2 variants were observed following two doses of vaccine in SLE patients. Follow-up booster doses increased humoral responses compared to baseline, but they remained lower, with poorer neutralisation capacity against most strains, compared to healthy individuals after three or more doses. Analysis of memory B-cell subsets in SLE patients revealed an increase of SARS-CoV-2-specific isotype unswitched IgM+ over SARS-CoV-2-specific isotype switched IgG+/IgA+ memory B-cells compared to healthy individuals. Culturing healthy naive B-cells with high levels of IFNα, a hallmark of SLE pathogenesis, prevented B-cells from switching to IgG under IgG-polarizing conditions., Conclusion: SLE patients' protection against SARS-CoV-2 is overall impaired compared to healthy individuals and is associated with a class switch defect possibly due to chronic exposure of B-cells to IFNα., (© The Author(s) 2024. Published by Oxford University Press on behalf of the British Society for Immunology.)