An active comparator study has shown that injections of daclizumab high-yield process (HYP), administered every 4 weeks, are more effective than weekly IFN-β1a injections at reducing relapse rates in patients with multiple sclerosis. However, the two drugs were comparable in terms of their effects on disability progression, and adverse events were more common in the daclizumab HYP group than in the IFN-β1a group, indicating that the choice of treatment is likely to be dictated by a variety of factors in addition to efficacy.