Phase 3b Study in Patients With Severe Asthma Treated With Tezepelumab

This study aims to explore the potential for Tezepelumab-treated severe asthmatic patients to effectively and safely reduce their background maintenance medication while maintaining asthma symptom control.

Inclusion Criteria: 1. Provision of informed consent prior to any study-specific procedures. 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. Age 2. Patient must be aged 12-80 years old, inclusively, at the time of Visit 1(Week -1 to Week 0) For those patients, who are 17 on the day of Visit 1(Week -1 to Week 0) but will turn 18 after this day, will be considered an adolescent for the purposes of this study. Type of Patient and Disease Characteristics 3. Documented history of physician-diagnosed asthma prior to Visit 1 • Evidence of asthma as documented within 12 months prior to Visit 1 by either: (1) a positive bronchodilator (BD) responsiveness (reversibility), defined as an increase in FEV1 of ≥12% and ≥200 mL after inhalation of a bronchodilator, or an increase in FEV1 of ≥12% and ≥200 mL from baseline after 4 weeks of anti-inflammatory treatment containing ICS; or (2) a positive bronchial provocation test, defined as a decrease in FEV1 of ≥20% after inhalation of a provoking agent, commonly methacholine or histamine; or (3) average daily diurnal variability in PEF of \>10%, calculated over at least 7 consecutive days as the sum of the daily diurnal PEF variability values divided by the number of days; or (4) a excessive variation in lung function between visits, defined as change in FEV1 of ≥12% and ≥200 mL. In the absence of any such positive record in the previous 12 months, variable expiratory airflow must be confirmed and documented at Visit 1 4. Documented current maintenance treatment with MD/HD ICS + LABA with up to one additional controller • Other acceptable asthma controller includes LTRA, LAMA or theophylline 5. On stable MD/HD ICS (\>250μg fluticasone propionate dry powder formulation equivalents total daily dose) + LABA stable for ≥2 months prior to enrollment 6. On stable LTRA or LAMA or theophylline (≥2 weeks) is allowed 7. In asthma uncontrolled status at Visit 1, asthma uncontrolled defined as at least one of the following: 1. Documented ACQ-5 ≥ 1.5 at Visit 1, Or 2. Documented exacerbation in the year prior to Visit 1 in either situation as below: • ≥ 2 times of symptomatic worsening requiring systemic corticosteroid (including a temporary increase in a stable oral corticosteroid background dose) for at least 3 days; a single depo-injectable dose of corticosteroids will be considered equivalent to a 3-day course of systemic corticosteroids , OR, • At least one emergency room visit (defined as evaluation and treatment for \