An Open-Label, Randomized, Multicenter, Active-Controlled, Parallel-Group Study to Evaluate the Safety, Tolerability, and Efficacy of BIIB017 in Pediatric Subjects Aged 10 to Less Than 18 Years for the Treatment of Relapsing-Remitting Multiple Sclerosis, With Optional Open-Label Extension

Part 1:

– Must have a diagnosis of RRMS as defined by the revised consensus definition for
pediatric MS.

– Must have an EDSS score between 0.0 and 5.5.

– Must have experienced >= 1 relapse in the 12 months prior to randomization (Day 1) or
>= 2 relapses in the 24 months prior to randomization (Day 1) or have evidence of
asymptomatic disease activity (Gd-enhancing lesions) on brain MRI in the 6 months
prior to randomization (Day 1).

Part 2:

• Participants who completed the study treatment in Part 1 (Week 96 Visit), as per
protocol.

Key Exclusion Criteria:

Part 1:

– Primary progressive, secondary progressive, or progressive relapsing. These conditions
require the presence of continuous clinical disease worsening over a period of at
least 3 months. Participants with these conditions may also have superimposed relapses
but are distinguished from relapsing participants by the lack of clinically stable
periods or clinical improvement.

– History of severe allergic or anaphylactic reactions or known drug hypersensitivity.

– Known allergy to any component of Avonex or BIIB017 formulation.

– Occurrence of an MS relapse that has occurred within 30 days prior to randomization
(Day 1) and/or the participant has not stabilized from a previous relapse prior to
randomization (Day 1).

– Any previous treatment with PEGylated human IFN β-1a.

Part 2:

– Any significant changes in medical history occurring after enrollment in Part 1,
including laboratory test abnormalities or current clinically significant conditions
that, in the opinion of the Investigator, would have excluded the participant’s
participation in Part 1. The Investigator must re-assess the participant’s medical
fitness for participation and consider any factors that would preclude treatment.

– The participant could not tolerate BIIB017 in Part 1.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply”