Knowledge gained from this project will be used to determine LAIV safety in children with CF, a patient population in whom influenza has major health impacts and who could greatly benefit from a recommendation for LAIV preferential use. Moreover, the intranasal route of administration should make this vaccine more acceptable to patients that need yearly vaccination, thereby potentially increasing vaccination coverage. Patients with CF are also the population in whom the risk of adverse events with LAIV is the highest, given their baseline respiratory condition and inflammatory dysregulation. Therefore, if LAIV is well tolerated in this population, the investigators could generalize LAIV preferential use to other pediatric populations with chronic conditions.