This is a randomised, double-blind, parallel group, placebo-controlled study designed to evaluate the efficacy and safety of a fixed 30 mg dose of benralizumab administered subcutaneously for patients with a history of asthma exacerbations and uncontrolled asthma receiving medium to high-dose inhaled corticosteroid plus long-acting β2-agonist (ICS-LABA) with or without oral corticosteroids and additional asthma controllers.

Approximately 666 patients will be randomised. Patients will be stratified by country/region, age group (adult or adolescent), and peripheral blood eosinophil count at time of Visit 1 (<300 or ≥300 cells/μL).All the patients will be randomised to either placebo or benralizumab (1:1 ratio) for a 48-weeks treatment, every 4 weeks for the first 3 doses and then every 8 weeks thereafter.

Key Inclusion Criteria:

1. Written informed consent, and assent when applicable for study participation must be obtained prior to any study related procedures being performed (local regulations are to be followed in determining the assent/consent requirements for children and parent[s]/guardian[s]) and according to international guidelines and/or applicable local guidelines.

2. Female and male aged 12 to 75 years, inclusively, at the time of Visit 1. For those patients, who are 17 on the day of Visit 1 but will turn 18 after this day, will be considered an adolescent for the purposes of this trial.

3. History of physician-diagnosed asthma requiring treatment with medium-to-high dose ICS (>250μg fluticasone propionate dry powder formulation equivalents total daily dose) and a LABA, for at least 6 months prior to Visit 1.

4. Additional maintenance asthma controller medications that are locally approved in a country for the treatment of asthma (e.g., leukotriene receptor antagonists (LTRAs), tiotropium, chromone, theophylline, oral corticosteroid), and have been used for at least 30 days prior to Visit 1 are allowed.

5. At least 2 documented asthma exacerbations in the 12 months prior to the date informed consent, and assent when available, during the treatment of medium-to-high dose ICS-LABA that required use of a systemic corticosteroid or a temporary increase from the patient's usual maintenance dose of oral corticosteroid. For patients who are re-screened within 30 days of their screen failure date, the calculation of the 12 month period should be done from the original informed consent, and assent when applicable date.

6. Documented post-bronchodilator (post-BD) reversibility in FEV1 of >12% and >200 mL in FEV1 within 12 months prior to Visit 1. If historical documentation is not available, reversibility must be demonstrated and documented at Visit 2.

7. Fulfilment of at least 1 of the following conditions over the 7 days prior to randomization:

   • >2 days with a daytime or night time symptoms score >1
   • Rescue Short-acting β2 agonist (SABA) use on >2 days
   • ≥1 nocturnal awakening due to asthma

8. Pre-bronchodilator (Pre-BD) FEV1 of <80% predicted (<90% predicted for patients aged 12 to 17 years) at Visit 2.

9. ACQ-6 score > = 1.5 at Visit 2.

Exclusion Criteria:

1. Known history of clinically important pulmonary disease other than asthma (e.g., active lung infection, chronic obstructive pulmonary disease (COPD), bronchiectasis, pulmonary fibrosis, cystic fibrosis, hypoventilation syndrome associated with obesity, lung cancer, alpha 1 anti-trypsin deficiency, and primary ciliary dyskinesia) or ever been diagnosed with pulmonary or systemic disease, other than asthma, that are associated with elevated peripheral eosinophil counts (e.g,. allergic bronchopulmonary aspergillosis/mycosis, Churg-Strauss syndrome, hypereosinophilic syndrome).

2. Known history of any disorder, including, but not limited to, cardiovascular, gastrointestinal, hepatic, renal, neurological, musculoskeletal, infectious, endocrine, metabolic, haematological, psychiatric, or major physical impairment that is not stable in the opinion of the Investigator and could:

   • Affect the safety of the patient throughout the study
   • Influence the findings of the studies or their interpretations
   • Impede the patient's ability to complete the entire duration of study.

3. Acute upper or lower respiratory infections requiring antibiotics or antiviral medication within 30 days prior to the date informed consent, and assent when applicable, is obtained or during the screening period.

4. Any clinically significant abnormal findings in physical examination, vital signs, haematology, clinical chemistry, or urinalysis during screening period, which in the opinion of the Investigator, may put the patient at risk because of his/her participation in the study, or may influence the results of the study, or the patient's ability to complete entire duration of the study.

5. Current smokers or former smokers with a smoking history of > 10 pack-years.

Qualified researchers can request access to anonymized individual patient-level data from AstraZeneca group of companies sponsored clinical trials via the request portal. All request will be evaluated as per the AZ disclosure commitment: https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

AstraZeneca will meet or exceed data availability as per the commitments made to the EFPIA Pharma Data Sharing Principles. For details of our timelines, please rerefer to our disclosure commitment at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.

When a request has been approved AstraZeneca will provide access to the de-identified individual patient-level data in an approved sponsored tool . Signed Data Sharing Agreement (non-negotiable contract for data accessors) must be in place before accessing requested information. Additionally, all users will need to accept the terms and conditions of the SAS MSE to gain access. For additional details, please review the Disclosure Statements at https://astrazenecagrouptrials.pharmacm.com/ST/Submission/Disclosure.