 This is a multi-centre, placebo-controlled, double-blind, parallel-group study to evaluate the efficacy and safety of mepolizumab adjunctive therapy in participants with severe eosinophilic asthma on markers of asthma control. The overall intent of the current study is to more fully explore the impact of mepolizumab on health-related quality of life HR-QoL and other measures of asthma control, including lung function. 