A Study on Mucosal Specific IgA Immunokinetics After Administration of Nasal Spray Live Attenuated Influenza Vaccine

Inclusion Criteria: * People aged 3 to 17 years old who voluntarily receive the live attenuated influenza nasal spray vaccine; * The participant themselves can comply with the protocol requirements and complete sample collection; * Obtain the consent of the participants' guardians and sign the informed consent form; Exclusion Criteria: * Axillary temperature \> 37.0°C on the day of enrollment; * Received any influenza vaccine within the past 2 years and plans to receive other influenza vaccines during the trial period; * Clinically diagnosed with influenza in a medical institution within the past year (with confirmed etiological diagnosis); * Individuals with known hypersensitivity to any ingredient contained in this product, including eggs, excipients, and gentamicin sulfate; * Individuals suffering from acute diseases, severe chronic diseases, acute exacerbations of chronic diseases, and fever; * Pregnant women; * Patients with Leigh syndrome who are being treated with aspirin or aspirin-containing medications; * Individuals with immunodeficiency or those undergoing immunosuppressive therapy; * Individuals with uncontrolled epilepsy and other progressive neurological diseases, or those with a history of Guillain-Barré syndrome; * Nasal abnormalities that, in the judgment of a clinician, may affect vaccination, individuals in the medication period for allergic rhinitis, or those currently receiving nasal spray administration; * Having received a live attenuated vaccine within 14 days prior to enrollment, or a subunit or inactivated vaccine within 7 days prior to enrollment; * Presence of other factors deemed unsuitable for participation in this study by the investigator.