This is a randomized, double-blind, multicenter, parallel-group Phase IIIb study with a fixed treatment period of 52 weeks. The purpose of this study is to compare BDA MDI with AS MDI on severe asthma exacerbations in adolescent participants aged 12 to < 18 years with a documented clinical diagnosis of asthma and at least one severe exacerbation in the prior year. Participants will administer randomized IMP as needed as they normally would with their own prescribed rescue inhaler.

The main purpose of this study is to see if taking benralizumab is effective in treating Severe Eosinophilic Asthma in patients 6 to 17 years old compared with placebo. Benralizumab is administered through a subcutaneous injection (shot). Participation in the study is divided into two parts. The first part will last up to 16 weeks or until an asthma attack or flare is experienced. The second part will last up to two years.