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Background This study evaluated the yearly risk of developing serious infections (SIs) with ofatumumab (OMB) treatment over a period of 6 years (cutoff date: 25-Sep-2023) in pwRMS.Methods Participants who received at least one dose of OMB in ASCLEPIOS I/II, APLIOS, APOLITOS or ALITHIOS were included, and data from OMB first dose analysed. SIs (infections classified by the investigator as serious adverse events under the System Organ Class of Infections and infestations) were analysed by risk categories including respiratory tract infections (RTls) (excluding COVID-19), COVID-19, appendicitis, urinary tract infections (UTls), herpes viral infections and others. Annualised rate of SIs for each year was estimated by negative binomial regression model, with cumulative infection count in each patient in the year as the response variable, year as a factor and time at risk in the year as an offset variable.Results Of 1969 participants included in the analysis (cumulative exposure, 8042.7 PYs), 115 participants (5.84%) had 130 SIs over 6 years. Most commonly reported SIs were COVID-19 (n=49; 2.49%), UTI (n=16; 0.81%), lower RTI (n=16; 0.81%), and appendicitis (n=15; 0.76%). The annualised rates (95% Cl) of SIs excluding COVID-19 were low throughout 6 years of treatment (Year 1, 0.013 [0.008–0.021); Year 2, 0.010 [0.006–0.017); Year 3, 0.011 [0.006–0.018]; Year 4, 0.006 [0.003–0.013]; Year 5, 0.007 [0.003–0.017]; and Year 6, 0.010 [0.004–0.025)).Conclusion The results show that long-term use of ofatumumab did not increase the risk of SIs over 6 years, supporting the favourable long-term safety profile of ofatumumab in pwRMS.