| Summary: | Abstract Background In the PRISMS study, interferon beta-1a subcutaneously (IFN β-1a SC) reduced clinical and radiological disease burden at 2 years in patients with relapsing–remitting multiple sclerosis. The study aimed to characterize efficacy of IFN β-1a SC 44 μg and 22 μg three times weekly (tiw) at Year 1. Methods Exploratory endpoints included annualized relapse rate (ARR), 3-month confirmed disability progression (1-point Expanded Disability Status Scale increase if baseline was < 6.0 [0.5-point if baseline was ≥6.0]), active T2 lesions, and no evidence of disease activity (NEDA; defined as no relapses [subanalyzed by relapse severity], 3-month confirmed progression, or active T2 lesions). Effect of IFN β-1a SC in prespecified patient subgroups was also assessed. Results Patients were randomized to IFN β-1a 22 μg (n = 189), 44 μg (n = 184), or placebo (n = 187). At 1 year, IFN β-1a SC tiw reduced ARR (p < 0.001), risk of disability progression (p ≤ 0.029), and mean number of active T2 lesions per patients per scan (p < 0.001) versus placebo. Clinical and radiological benefits were seen as early as Month 2 and 3. Outcomes in subgroups were consistent with those in the overall population. More patients treated with IFN β-1a SC tiw achieved NEDA status, versus placebo, regardless of relapse severity (p ≤ 0.006). Conclusion Clinical, radiological, and NEDA outcomes at Year 1 were consistent with Year 2 results. Treatment efficacy was consistent in pre-specified patient subgroups.
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