Efficacy and Safety Study of Mepolizumab Adjunctive Therapy in Participants With Severe Eosinophilic Asthma on Markers of Asthma Control

Inclusion Criteria

• Age: At least 12 years of age at the time of signing the informed consent/assent (For those countries where local regulations permit enrolment of adults only, participant recruitment will be restricted to those who are >=18 years of age)
• Inhaled Corticosteroid: A well-documented requirement for regular treatment with high dose inhaled corticosteroid (ICS) in the 12 months prior to Visit 1 with or without maintenance oral corticosteroids (OCS). For participants >=18 years old: ICS dose must be >=880 micrograms (mcg)/day fluticasone propionate (FP) (exactuator) or equivalent daily. For ICS/long-acting beta-2-agonist (LABA) combination preparations, the highest approved maintenance dose in the local country will meet this ICS criterion. For participants >=12 to =440 mcg/day FP (ex-actuator) or equivalent daily. For ICS/LABA combination preparations, the mid-strength approved maintenance dose in the local country will meet this ICS criterion
• Controller Medication: Current treatment with an additional controller medication, besides ICS, for at least 3 months or a documented failure in the past 12 months of an additional controller medication for at least 3 successive months (e.g. LABA, leukotriene receptor antagonist [LTRA], or theophylline)
• Eosinophilic asthma: Prior documentation of eosinophilic asthma or high likelihood of eosinophilic asthma as per Randomisation Criteria 1 and 2
• FEV1: Persistent airflow obstruction as indicated by : For participants >=18 years of age at visit 1, a pre-bronchodilator FEV1 =10 pack years (number of pack years = (number of cigarettes per day/20) x number of years smoked). A former smoker is defined as a participant who quit smoking at least 6 months prior to Visit 1.
• Concurrent Respiratory Disease: Presence of a known pre-existing, clinically important lung condition other than asthma. This includes current infection, bronchiectasis, pulmonary fibrosis, bronchopulmonary aspergillosis, or diagnoses of emphysema or chronic bronchitis (chronic obstructive pulmonary disease other than asthma) or a history of lung cancer.
• Malignancy: A current malignancy or previous history of cancer in remission for less than 12 months prior to screening (Participants that had localized carcinoma of the skin which was resected for cure will not be excluded).
• Liver Disease: Known, pre-existing, unstable liver disease (as defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminaemia, esophageal or gastric varices or persistent jaundice), cirrhosis, and known biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones).
• Cardiovascular: Participants who have severe or clinically significant cardiovascular disease uncontrolled with standard treatment. Including but not limited to: (a) known ejection fraction of =450 milliseconds (msec) or QTc(F) >=480 msec for participants with Bundle Branch Block at Visit 1.
• Alcohol/Substance Abuse: A history (or suspected history) of alcohol misuse or substance abuse within 2 years prior to Visit 1.
• Immunodeficiency: A known immunodeficiency (e.g. human immunodeficiency virus [HIV]), other than that explained by the use of corticosteroids taken as therapy for asthma.
• Xolair: Participants who have received omalizumab (Xolair) within 130 days of Visit 1.
• Other Monoclonal Antibodies: Participants who have received any monoclonal antibody (other than Xolair) to treat inflammatory disease within 5 half-lives of Visit 1.
• Investigational Medications: Participants who have received treatment with an investigational drug within the past 30 days or five terminal phase half-lives of the drug whichever is longer, prior to Visit 1 (this also includes investigational formulations of marketed products).
• Hypersensitivity: Participants with allergy/intolerance to a monoclonal antibody or biologic.
• Pregnancy: Participants who are pregnant or breastfeeding. Patients should not be enrolled if they plan t