This is a single-center, open-label, single-arm clinical trial designed to evaluate the mucosal and systemic immune responses induced by an intranasal influenza live attenuated vaccine, and to explore the correlation between the two. The study plans to recruit 60 healthy volunteers aged 14-17 years, with a male-to-female ratio of 1:1. Participants and their guardians must be able and willing to comply with the clinical trial protocol and provide informed consent. Eligible participants will receive a single 0.2 mL dose of LAIV prior to the influenza season. Information on participants' historical vaccination records, baseline demographic data, and past health status will be collected. Nasal specimens (nasal secretions and nasal mucosal cells) and blood samples (serum and PBMCs) will be collected on Day 0 (before vaccination), Day 7, and Day 28 after vaccination for transcriptome sequencing and immunogenicity analysis. In addition, fecal samples will be collected on Day 0 (before vaccination), Day 7, and Day 28 after vaccination for intestinal microbiota detection.