GlaxoSmithKline plc announced that both co-primary endpoints and all secondary endpoints were met in a pivotal phase III study investigating the efficacy and safety of mepolizumab, an IL-5 antagonist, in patients with relapsing and refractory Eosinophilic Granulomatosis with Polyangiitis (EGPA), a rare disease characterised by widespread inflammation in the walls of small blood vessels (vasculitis).