Patient description: The patient is a 15-year-old boy with asthma diagnosed a year ago. He presents with shortness of breath, chest tightening and cough. According to his mother, he didn't respond to the usual corticosteroid inhaler. He was admitted to the emergency department with diagnosis of severe asthma exacerbation. He is a candidate for general corticosteroid therapy. Spirometry revealed a forced expiratory volume in the first second (FEV1) of 60% of the predicted. His past medical history is non-significant. His family history is significant for asthma in his mother and his uncle. He used to be treated with combination of inhaled corticosteroids and Zafirlukast.

Clinical trial eligibility criteria: eligible ages (years): 12.0-999.0,  Asthma 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 <=17 years old: ICS dose must be >=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 1 and 2 FEV1: Persistent airflow obstruction as indicated by : For participants >=18 years of age at visit 1, a pre-bronchodilator FEV1 <80% predicted (National Health and Nutrition Examination Survey [NHANES III]) recorded at Visit 1. For participants 12-17 years of age at Visit 1: A pre-bronchodilator FEV1 <90% predicted (NHANES III) recorded at Visit 1 OR FEV1:FVC ratio <0.8 recorded at Visit 1 Exacerbation history: Previously confirmed history of two or more exacerbations requiring treatment with systemic Corticosteroid (CS) (intramuscular, intravenous, or oral), in the 12 months prior to visit 1, despite the use of high-dose inhaled corticosteroids (ICS). For participants receiving maintenance CS, the CS treatment for the exacerbations must have been a two-fold dose increase or greater Gender: Male or Eligible Female. To be eligible for entry into the study, females of childbearing potential must commit to consistent and correct use of an acceptable method of birth control listed in the protocol for the duration of the trial and for 4 months after the last study drug administration Informed Consent/Assent: Able to give written informed consent/assent prior to participation in the core study, which will the ability to comply with the requirements and restrictions listed in the consent/assent form and in this protocol. Participants must be able to read, comprehend, and write at a level sufficient to complete study related materials. Written informed consent must be obtained from ALL patients/legally authorized representative(s); for patients 12-17 years old, written informed assent must be obtained in addition to the legally authorized representative(s)' consent French participants: In France, a participant will be eligible for in this study only if either affiliated to or a beneficiary of a social security category  Smoking history: Current smokers or former smokers with a smoking history of >=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 <30% OR (b) severe heart failure meeting New York Heart Association Class IV classification OR (c) hospitalised in the 12 months prior to Visit 1 for severe heart failure meeting New York Heart Association Class III OR (d) angina diagnosed less than 3 months prior to Visit 1 or at Visit 1 Other Concurrent Medical Conditions: Participants who have known, pre-existing, clinically significant endocrine, autoimmune, metabolic, neurological, renal, gastrointestinal, hepatic, haematological or any other system abnormalities that are uncontrolled with standard treatment Eosinophilic Diseases: Participants with other conditions that could lead to elevated eosinophils such as Hypereosinophilic Syndromes, including Churg-Strauss Syndrome (Eosinophilic Granulomatosis with Polyangiitis [EGPA]), or Eosinophilic Esophagitis. Participants with a known, pre-existing parasitic infestation within 6 months prior to Visit 1 are also to be excluded Electrocardiogram (ECG) Assessment: QT interval corrected for heart rate by Fridericia's formula (QTc(F)) >=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