Clinical Trial to Evaluate the Protective Efficacy and Safety of a Nasal Spray Live Attenuated Influenza Vaccine (LAIV) in Adults Aged 18-59 Years Post-Vaccination

Inclusion criteria

• Healthy participants aged 18-59 years
• Capable of providing informed consent in person
• Willing and able to comply with all clinical trial requirements

Exclusion criteria

• Axillary temperature >37.0°C on enrollment day *
• Received any influenza vaccine within the past 6 months or plans to receive other influenza vaccines during the trial
• History of laboratory-confirmed influenza (by clinical, serological, or microbiological methods) within the past 6 months
• Female participants of childbearing potential with positive urine pregnancy test, currently breastfeeding, or planning pregnancy within 6 months
• Acute phase of any infectious disease/chronic illness within 3 days, or recent use (≤3 days) of antipyretics/analgesics/antihistamines *
• History of severe allergies requiring medical intervention (e.g., anaphylaxis, angioedema, Arthus reaction) or hypersensitivity to vaccine components (egg proteins, gentamicin sulfate, etc.)
• Known malignancies, autoimmune diseases (e.g., SLE, rheumatoid arthritis), or immunodeficiency (HIV, organ transplantation, etc.)
• Asplenia, functional asplenia, or any splenectomy history
• Use of immunosuppressants/immunomodulators (e.g., systemic corticosteroids >14 days) within 6 months or planned use during study
• Congenital anomalies affecting organ function, uncontrolled hypertension (≥140/90 mmHg despite treatment), or severe hepatic/renal diseases (e.g., diabetes-complicated)
• Active asthma or clinical remission for <12 months
• History or family history of neurological/psychiatric disorders (e.g., epilepsy, Guillain-Barré syndrome)
• Salicylate use (e.g., aspirin) within 30 days or planned use within 6 weeks post-vaccination
• Nasal abnormalities potentially affecting vaccine administration (e.g., active allergic rhinitis with medication, ongoing nasal sprays)
• Blood products/immunoglobulin administration within 3 months or planned use during trial
• Live-attenuated vaccines within 14 days or subunit/inactivated vaccines within 7 days prior to enrollment *
• Participation in other clinical trials within 1 month or concurrent involvement in interventional studies
• Any condition deemed by investigators to compromise trial integrity