Subjects who meet the eligibility criteria will participate in the following two treatment periods: FF/VI 100/25 mcg once-daily and placebo once-daily. Approximately 28 subjects will be enrolled in order to achieve 24 evaluable subjects. A 2-week treatment period will be followed by a 21-day monitoring/washout period before crossing over to the next treatment period. Total duration of each subject will be a maximum of 21 weeks. FeNO will be monitored up to 21 days after treatment with FF/VI together with FEV1 (up to 7 days).