The purpose of this study is to evaluate the antiviral effect, as measured by the time to alleviation of influenza symptoms and viral titer in nasopharyngeal secretions in adults with acute uncomplicated influenza A following administration of ZSP1273.

Inclusion Criteria:

1. Males and female subjects between 18-65 years (Both inclusive).

2. Patients with a diagnosis of influenza virus A infection confirmed by all of the following:

   • Positive Rapid Antigen Test (RAT) with throat swabs;and

   • Fever≥38.0ºC (axillary) in the predose examinations;and

   • At least one of the following general systemic symptoms and respiratory symptoms respectively associated with influenza are present with a severity of moderate or greater:

     • General systemic symptoms:Headache,Feverishness or chills,Muscle or joint pain,Fatigue;
     • Respiratory symptoms:Cough,Sore throat,Nasal congestion.

3. The time interval between the onset of symptoms and the enrollment is≤48 hours. The onset of symptoms is defined as:

   • Time of the first increase in body temperature(axillary temperature≥38.0ºC),or
   • Time when the patient experiences at least one general or respiratory symptom.

4. Subjects who agree to use an appropriate method of contraception during the study and up to 6 months after drug withdrawal.

5. Signature of a dated Informed Consent Form (ICF) indicating that the subject has been informed of all the relevant aspects(including adverse events) of the trial prior to enrollment.

Exclusion Criteria:

1. Known hypersensitivity and/or allergy to some drugs and food,especially for the composition that is similar to ZSP1273;

2. Dysphagia or any medical history in gastrointestinal that interferes with the absorption of drugs.

3. Use of the following medications within 7 days prior to screening:

   • Influenza antiviral medication:oseltamivir,peramivir,famivir,abidol,amantadine or rimantadine.
   • Chinese patent medicine or herbal medicine with antiviral effect.

4. Patients who have received influenza vaccine within 6 months prior to enrollment.

5. Presence of clinically significant abnormalities in ECG .

6. Chest X - ray examination confirmed bronchitis,pneumonia,pleural effusion or pulmonary interstitial lesions.

7. Patients who have experienced respiratory tract infection,Otitis media,nasosinusitis.

8. White blood cells(WBC)>10.0×109/L at screening.

9. Subject who produces purulent sputum or has suppurative tonsillitis.

10. Patients with severe or uncontrollable underlying diseases:blood disorders,severe chronic obstructive pulmonary disease(COPD),liver disorders(ALT or AST≥3 ULN,total bilirubin≥1.5 ULN),kidney disorders(serum creatinine>177μmol/L or 2mg/dL),chronic congestive heart failure(NYHA III-IV),mental disorders.

11. Immunodeficiency,including malignant tumor,organ or marrow transplant,human immunodeficiency virus [HIV] infection,or patients receiving immunosuppressant therapy 3 months prior to enrollment.

12. Concomitant therapy with aspirin or salicylic acid.

13. Morbid obesity(Body mass index [BMI]≥30kg/m2).

14. Known history of alcohol abuse or drug abuse.

15. Pregnancy or breastfeeding at screening and during the study.All female subjects of childbearing potential must have a negative urine pregnancy test at screening and during the trial.

16. Have received any other investigational products within 3 months prior to dosing.

17. Subjects who should not be included in the study in the opinion of the Investigator.