A Multicenter, Parallel-group, Double-blind, 2-Arm, Phase III Study to Investigate the Efficacy and Safety of Anifrolumab Administered as Subcutaneous Injection and Added to Standard of Care Compared With Placebo Added to Standard of Care in Adult Participants With Idiopathic Inflammatory Myopathies (Polymyositis and Dermatomyositis)

The purpose of this multicenter, randomized, placebo-controlled and double-blind study is to evaluate the efficacy and safety of subcutaneous anifrolumab compared with placebo on the overall disease activity in participants with moderate to severe Idiopathic Inflammatory Myopathies (IIM) \[polymyositis (PM) or dermatomyositis (DM)\] while receiving standard of care (SoC) treatment.