A Multicenter, Open-Label, Extension Study to Evaluate the Long Term Safety and Efficacy of BIIB019, Daclizumab High Yield Process (DAC HYP), Monotherapy in Subjects With Multiple Sclerosis Who Have Completed Study 205MS301

The primary objective of the study is to assess the safety and tolerability of long-term treatment with BIIB019 (Daclizumab High Yield Process; DAC HYP) monotherapy in participants with relapsing remitting multiple sclerosis (RRMS) who completed Study 205MS301 (NCT01064401), Study 205MS203 (NCT01051349) or Study 205MS302 (NCT01462318). Secondary objectives of this study in this study population are as follows: To describe MS-related outcomes, including MS relapse, disability progression, MS lesion formation, and participant-reported impact of MS, following long-term treatment with DAC HYP To assess the long-term immunogenicity of DAC HYP administered by prefilled syringe (PFS) To assess the safety, tolerability, and efficacy of switching to DAC HYP in participants previously on long-term treatment with interferon β-1a (Avonex) in Study 205MS301(NCT01064401).