(DECIDE)

Treatment tested

• Daclizumab

  Interleukin-2 receptor inhibitor

Compared with

• Interferon beta-1a

  Interferon alpha/beta receptor agonist

Placebo or sham

• Interferon beta-1a Placebo
• Daclizumab High Yield Process Placebo

Other measures (5)

Key Inclusion Criteria: * Must have a confirmed diagnosis of Relapsing Remitting Multiple Sclerosis (RRMS), and a cranial magnetic resonance imaging (MRI) demonstrating lesion(s) consistent with MS * Must have a baseline Expanded Disability Status Scale (EDSS) between 0.0 and 5.0, inclusive * Male subjects and female subjects of childbearing potential must be willing to practice effective contraception during the study and be willing and able to continue contraception for 4 months after their last dose of study treatment Key Exclusion Criteria: * Known intolerance, contraindication to, or history of non-compliance with Avonex® 30 µg * History of treatment with Daclizumab High Yield Process (Dac HYP) * History of malignancy * History of severe allergic or anaphylactic reactions * Known hypersensitivity to study drugs or their excipients * History of abnormal laboratory results indicative of any significant disease * History of human immunodeficiency virus (HIV) or other immunodeficient conditions * History of drug or alcohol abuse (as defined by the Investigator) within the 2 years prior to randomization * History of seizure disorder or unexplained blackouts OR history of a seizure within 6 months prior to Baseline * History of suicidal ideation or an episode of clinically severe depression (as determined by the Investigator) within 3 months prior to Day 1 * An MS relapse that has occurred within the 50 days prior to randomization AND/OR the subject has not stabilized from a previous relapse prior to randomization * Known history of, or positive screening test result for hepatitis C virus or hepatitis B virus * Varicella or herpes zoster virus infection or any severe viral infection within 6 weeks before screening * Exposure to varicella zoster virus within 21 days before screening NOTE: Other protocol-defined Inclusion/Exclusion criteria may apply.

The primary study objective is to test the superiority of Daclizumab High Yield Process (DAC HYP) compared to interferon β 1a (IFN β-1a) in preventing multiple sclerosis (MS) relapse in participants with relapsing remitting multiple sclerosis. The secondary study objectives are to test the superiority of DAC HYP compared to IFN β-1a in slowing functional decline and disability progression and maintaining quality of life in this participant population.