Inclusion Criteria:  Male or female Chinese aged 18-55 years (inclusive) at their enrollment of the study (signing the study consent form).  Clinical definite diagnosis of RMS according to the 2017 Revised McDonald criteria (Thompson et al 2018, and the documentation prior to their enrollment to the study (signing the study consent form) of:  Two documented relapses during the past 2 years, or One documented relapse during the last year, or A positive Gd-enhancing MRI scan during the year prior to Screening. Note: Screening MRI scan may be used if no positive Gd-enhancing scan exists from prior year. Disability status with an EDSS score of 0 - 5.5 (inclusive) at Screening. Neurologically stable within 1 month prior to both Screening and Baseline (including no MS relapse in this period).  Exclusion Criteria:  Participants with primary progressive MS (PPMS) or secondary progressive MS (SPMS) without disease activity Participants meeting criteria for neuromyelitis optica spectrum disorder (NMOSD) Pregnant or nursing (lactating) women Women of child-bearing potential unless using effective methods of contraception while taking study treatment and for at least 6 months after stopping medication Participants with an active chronic disease of the immune system other than MS Participants with neurological findings consistent with PML or confirmed PML Participants with active hepatitis B disease Participants with active systemic infections (including but not limited to active COVID-19 infection) or known to have AIDS or to test positive for HIV antibody at Screening Participants at high risk of developing or having reactivation of syphilis or tuberculosis Have received any live or live-attenuated vaccines within four weeks prior to first study drug administration Have been treated with medications as specified or within timeframes specified in the protocol Any other disease or condition that could interfere with participation in the study according to the study protocol, or with the ability of the participants to cooperate and comply with the study procedures.  Other protocol-defined inclusion/exclusion criteria may apply.