Aim 3: Assess LAIV safety in patients with CF: Compare the incidence of severe AEFI following LAIV in children with CF vaccinated with LAIV during the previous season (n = 70) compared to those without prior vaccination with LAIV (n = 45). Using a self-controlled case-series design, the investigators will compare the incidence of AEFI during the at-risk period (Day 1-28 post LAIV) and non at-risk period (Days 29-56). These incidence rate ratios will be compared in children with CF who are LAIV experienced and LAIV naïve.