Due to a change in Biogen Idec's medical research plans.

The primary objective of the study is to evaluate, in participants with RMS, safety and tolerability (as defined by the frequency of adverse events [AEs] of flu-like symptoms [FLS; chills, pyrexia, myalgia, and asthenia], injection site reactions [ISRs], and injection site reaction pain [ISR-P]) over 6 months of treatment (the active comparator period) with BIIB017 125 μg subcutaneously (SC) every 2 weeks versus standard-of-care SC interferon-beta (IFN-β) therapy. Secondary objectives of this study are to assess the following measures during the first (6-month) period of the study in participants treated with BIIB017 versus standard-of-care SC IFN-β therapy: patient-reported treatment satisfaction using the following patient-reported outcome measures (PROMs): Treatment Satisfaction Questionnaire for Medication (TSQM-9), Adapted MS Treatment Concerns Questionnaire (MSTCQ), Adapted MSTCQ Side Effects Score, Pain using a visual analog scale (VAS) diary and the McGill Pain Questionnaire Short Form (SF-MPQ), the treatments' impact on RMS using the following PROMs: Multiple Sclerosis Impact Scale (MSIS-29), Modified Fatigue Impact Scale-5 Item (MFIS-5), EuroQol Group 5-Dimension 3-Level Version (EQ-5D-3L), Health-Related Productivity Questionnaire (HRPQ), Beck Depression Inventory, second edition (BDI-II), participant adherence to study treatment, clinical status as measured by the Expanded Disability Status Scale (EDSS) and relapse activity, safety and tolerability of study treatment after a change in standard-of-care SC IFN-β therapy and the immunogenicity profiles of participants changing from standard-of-care SC IFN-β to BIIB017.

Key Inclusion Criteria:

• Must have a confirmed diagnosis of Relapsing Multiple Sclerosis (RMS), as defined by McDonald criteria.
• An Expanded Disability Status Scale (EDSS) score between 0 and 5.0.
• On continual treatment for ≥6 months with a single standard-of-care subcutaneous (SC) interferon beta (IFN-β) therapy, including IFN β-1b 0.25 mg SC every other day or IFN β-1a 44 μg SC 3 times weekly, and from a clinical perspective be able to continue this therapy (i.e., no significant untoward events attributed to IFN therapy that would preclude continuation of the existing IFN therapy).
• A candidate for change to BIIB017 therapy (candidacy for therapy change is determined by the treating physician; however, it is recommended to exclude patients with high disease activity and who are candidates for escalation therapy according to local guidelines).
• Patients who are randomized to their current standard-of-care IFN-β therapy for the first 6 months of the study must be willing to receive their treatment via the formulation provided in the study (i.e., Rebif 44 μg in a prefilled syringe or Betaferon/Betaseron 0.25 mg in single-use vials of lyophilized powder accompanied by a prefilled single-use diluent syringe).

Key Exclusion Criteria:

• Primary progressive, secondary progressive, or progressive relapsing MS.
• History of inadequate response to SC IFN therapy (as determined by the treating physician).
• History of severe allergic or anaphylactic reactions or known hypersensitivity to study drug or its excipients. - Known allergy to any component of the BIIB017 formulation.
• History of any clinically significant (as determined by the Investigator) cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal, or other major disease that would preclude participation in a clinical study.
• History of hypersensitivity or intolerance to acetaminophen, ibuprofen, naproxen, or aspirin that would preclude use of at least one of these during the study.
• An MS relapse that has occurred within the 50 days prior to randomization and/or lack of stabilization from a previous relapse prior to randomization.
• Any previous treatment with BIIB017.
• Treatment with other agents for MS.

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