The literature demonstrates a significant impact of influenza on the disease course of children with cystic fibrosis (CF) and superior efficacy of live-attenuated influenza vaccine (LAIV - Flumist®) compared to trivalent inactivated vaccine (TIV) in healthy and asthmatic children and adolescents. LAIV has recently been approved for use in Canada in people aged 2-59 years. CF is described as a hyper-inflammatory disorder, with abnormal inflammatory signaling, excessive inflammatory response, and impairment in the resolution of inflammation that could be a risk for the development of adverse events after LAIV. Given the impact of influenza in CF patients, the likelihood of superior protection of LAIV, the hyper-inflammatory status of CF patients that could increase the risk of adverse events, and the scarcity of data on the safety of LAIV use in this population, the assessment of LAIV's safety profile in CF patients is necessary to determine whether the anticipated benefits associated with LAIV use will outweigh potential risks, mainly respiratory deterioration. Our study specifically aims to: