The aim of this study is to evaluate the clinical efficacy and safety of inhaled zanamivir in treatment of influenza A and B virus infections in China.

Inclusion Criteria:

• Who had fever (>38.0ºC)
• At least two of the following symptoms: chills, headache, myalgia, fatigue, nasal symptoms, sore throat, cough
• Started therapy within 48 hours of onset of influenza-like illness
• Written informed consent

Exclusion Criteria:

• Respiratory diseases, such as asthma or COPD
• Woman with a positive urine pregnancy test
• Woman without contraception during the study
• Allergic to zanamivir, Paracetamol or lactose
• WBC ≥ 10.5×109/L; neutrophil percentage ≥ 80%
• Hepatic function impairment: AST ≥ 2×ULN, ALT ≥ 2×ULN
• Renal function impairment: Cr > 221μmol/L
• Influenza vaccination in the 12 months prior the beginning of the study
• History of tumor, psychiatric disorders, epilepsy or drug abuse
• Patients receiving corticosteroids, immunosuppressants
• HIV positive