Study 1 compared ZINBRYTA to 30 mcg weekly intramuscular doses of AVONEX in 1841 patients. The study included RMS patients who had either: 1) at least 2 relapses during the prior 3 years and at least one relapse in the year prior to randomization ; or 2) one or more clinical relapses and one or more new T1 gadolinium (Gd)-enhancing or T2 hyperintense MRI lesions within the prior 2 years with at least one of these events in the prior 12 months. Patients with progressive forms of multiple sclerosis or an Expanded Disability Status Scale (EDSS) score greater than 5 were excluded. Treatment continued for up to 144 weeks until the last enrolled patient completed 96 weeks of treatment. Clinical assessments were to occur every 12 weeks and after relapse events. MRI scans were performed at Week 24 and Week 96.