Decision to stop the trial was based on long-term difficulties in fulfilling our enrolment commitments and changes in paediatric MS landscape which no longer support placebo-controlled trials.Decision to stop study was not based on safety concerns.

The main objective of the study is to evaluate the efficacy of dimethyl fumarate (Tecfidera) and peginterferon beta-1a (Plegridy), both compared with placebo, in pediatric participants with RRMS. The other objectives of this study are to evaluate the safety and tolerability of dimethyl fumarate and peginterferon beta-1a and to assess the effect of dimethyl fumarate and peginterferon beta-1a, both compared with placebo, on additional clinical and radiological measures of disease activity.

Participants will be randomized in a 1:2:2 ratio to receive the double-blind study treatment (Dimethyl Fumarate, Peginterferon Beta-1a, and placebo). Participants experiencing a confirmed relapse or disability progression or high lesion burden on MRI will have the option to discontinue the blinded study treatment and switch to an alternative therapy or open-label BG00012.

Key Inclusion Criteria:

• 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 5.0.
• Must have a body weight of ≥30 kg
• Must have experienced ≥1 relapse in the 12 months prior to randomization (Day 1), or must have evidence of asymptomatic disease activity seen on MRI in the 6 months prior to randomization, or ≥2 relapses in the 24 months prior to randomization (Day 1). Relapse is defined as the occurrence of a clinical demyelination event regardless of whether the event is a first or subsequent demyelinating event.

Key Exclusion Criteria:

• Participants having primary progressive, secondary progressive, or progressive RMS.
• Disorders mimicking MS, such as other demyelinating disorders, systemic autoimmune disorders, metabolic disorders, and infectious disorders.
• History of clinically significant cardiovascular, pulmonary, GI, hepatic, renal, endocrinologic, hematologic, immunologic, metabolic, dermatologic, growth, developmental, psychiatric (including depression), neurologic (other than MS), and/or other major disease and/or laboratory abnormality indicative thereof, that would preclude participation in a clinical study
• Occurrence of an MS relapse within the 30 days prior to randomization (Day 1) and/or the subject has not stabilized from a previous relapse prior to randomization

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

In accordance with Biogen's Clinical Trial Transparency and Data Sharing Policy on https://www.biogentrialtransparency.com/

Our agreement is subject to confidentiality but generally the PI can publish, for non-commercial purposes only, results and methods of the trial, but no other Sponsor Confidential Information. PI must give Sponsor no less than 60 days to review any manuscript for a proposed publication and must delay publication for up to an additional 90 days thereafter if Sponsor needs to file any patent application to protect any of Sponsor's intellectual property contained in the proposed publication.