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Background We aimed to assess antibody responses and COVID-19 outcomes after vaccination in people with multiple sclerosis (pwMS) receiving disease-modifying therapies.Methods NevroVAX is a Norwegian multicentre cohort study including 3559 pwMS and 449 healthy controls (HCs) who received at least one dose of BNT162b2 (Pfizer-BioNTech), mRNA-1273 (Moderna) or ChAdOx1 (AstraZeneca/Oxford) between January 2021 and December 2022. Data from records, registries, questionnaires and blood samples collected June 2021–November 2023 were analysed. Primary outcomes were humoral immune responses assessed by seroconversion (anti-spike and anti-receptor-binding domain (RBD) IgG ≥5 binding antibody units/mL). Secondary outcomes included quantitative anti-RBD IgG levels, breakthrough SARS-CoV-2 infection, COVID-19-related hospitalisation and death. Associations with breakthrough infection were evaluated using multivariable logistic regression.Results Among 3559 pwMS, 1201 received anti-CD20 monoclonal antibodies and 324 sphingosine-1-phosphate receptor (S1PR) modulators. After three vaccine doses, seroconversion was observed in 43.0% of anti-CD20-treated patients and 48.4% of S1PR-treated patients. In multivariable analysis, seroconversion was associated with lower risk of breakthrough infection (OR 0.67, 95% CI 0.58 to 0.78). During follow-up, 58 pwMS (1.6%) were hospitalised for COVID-19; 4 (0.1%) required non-invasive ventilatory support, no patients required invasive ventilation and no deaths occurred.Conclusions Humoral vaccine responses were impaired in pwMS receiving anti-CD20 or S1PR therapies, but severe COVID-19 was rare. These findings support continued vaccination programmes and tailored protective measures for immunomodulated populations.