Asthma exacerbation was defined as a worsening of asthma that led to any of the following: * Use of systemic corticosteroids for at least 3 days; a single depo-injectable dose of corticosteroids was considered equivalent to a 3-day course of systemic corticosteroids. * An emergency room (ER) or urgent care (UC) visit (defined as evaluation and treatment for \<24 hours in an ER or UC centre) due to asthma that required systemic corticosteroids (see above). * An inpatient hospitalisation (defined as admission to an inpatient facility and/or evaluation and treatment in a healthcare facility for ≥24 hours) due to asthma. AAER = number of exacerbations\*365.25 / (follow-up date - date of randomisation + 1) (where maximum follow-up time for a patient was approximately 52 weeks). AAER in the tralokinumab group was compared to that seen in the placebo group up to Week 52 using a negative binomial model; rate ratios and rate reductions are both presented for comparative statistical analyses.