Study to Assess the Tolerability, Safety and Efficacy of GP681 Powder for Oral Suspension

Inclusion Criteria:

1. Male or female participants aged 2 to 18 years (≥2 years and <18 years).

2. For participants aged 5 to 18 years (excluding 18 years): body weight ≥20 kg; forparticipants aged 2 to 5 years (excluding 5 years): 10 kg≤body weight <20 kg.

3. Diagnosed with influenza virus infection based on the following criteria: • Positiverapid antigen test (RAT) result from a throat or nasal swab for influenza virus (rapid nucleic acid tests or other rapid molecular diagnostic tests are alsoacceptable); and

• Fever at screening (axillary temperature ≥37.5°C). If antipyretics have beenadministered, axillary temperature should be ≥37.5°C at least 1 hour afteradministration, or fever (axillary temperature <37.5°C) that returns to ≥37.5°Cmore than 4 hours after antipyretic use; and

• At least one moderate or severe respiratory symptom at screening, includingcough and/or nasal congestion or runny nose.

4. Time interval between the onset of illness symptoms and enrollment is ≤48 hours. Onset of illness: defined as the time of the first temperature increase (axillarytemperature ≥37.5°C) or the time when at least one respiratory symptom related toinfluenza virus infection is first noticed by caregiver.

5. The participant's legal guardian agrees to the child's participation in the clinicalstudy and signs the informed consent form (ICF). Participants aged ≥8 years mustalso voluntarily sign the ICF.

6. The investigator assesses that the participant and/or the caregiver can comply withthe protocol requirements, follow-up visits, and complete all study procedures andevaluations, including diary card entries.

Exclusion Criteria:

1. Known allergy to the active ingredients or excipients of the investigational drugGP681.

2. Patients diagnosed with severe or critical influenza at screening: (1) Severeinfluenza cases were defined by the presence of one or more of the followingconditions: a. Breathing difficulty and/or increased respiratory rate: >30breaths/min for children >5 years old, >40 breaths/min for children aged 2-5 years;b. Consciousness alteration: slow response, somnolence, agitation, seizures, etc; c.Severe vomiting or diarrhea with moderate or severe dehydration; d. Pneumonia; e.Significant exacerbation of underlying diseases. (2) Critical influenza cases weredefined by the presence of one or more of the following conditions: a. Respiratoryfailure; b. Acute necrotizing encephalopathy; c. Septic shock; d. Multiple organdysfunction; e. Other severe clinical conditions requiring intensive care treatment. Note: Refer to the "Expert Consensus on Diagnosis and Treatment of Influenza inChildren (2020 Edition)" for the criteria of severe/critical influenza.

3. History of any gastrointestinal disease known to affect drug absorption (includingbut not limited to gastroesophageal reflux disease, chronic diarrhea, inflammatorybowel disease, intestinal tuberculosis, gastrinoma, short bowel syndrome, orpost-gastrectomy conditions).

4. Suspected or confirmed bronchitis, pleural effusion, or interstitial pneumonia viaclinical or radiological examination at screening.

5. Use of anti-influenza antiviral drugs within two weeks before screening (includingneuraminidase inhibitors, hemagglutinin inhibitors, and M2 ion channel blockers suchas oseltamivir phosphate, zanamivir, peramivir, favipiravir, arbidol, baloxavir,amantadine, or rimantadine, or other anti-influenza antiviral drugs approved by theNMPA).

6. Clinically relevant abnormal results in physical examination, 12-lead ECG, vitalsigns, hematology, clinical biochemistry, or urinalysis at screening, which in theinvestigator's judgment may pose a risk to the participant's safety, affect thestudy results, or impact the participant's ability to complete the study.

7. Acute respiratory tract infection, otitis media, or sinusitis within two weeksbefore screening.

8. Co-infection requiring systemic antibiotics or other systemic therapy at screening.

9. Known or suspected active primary or secondary immunodeficiency, including a historyof HIV infection or other severe immunodeficiencies.

10. Known or suspected congenital abnormalities of the heart or lungs, or severe primarydiseases affecting the cardiovascular, hepatic, renal, or hematopoietic systems, orevidence of active liver disease, including but not limited to jaundice or AST/ALTlevels exceeding two times the upper limit of normal (ULN) at screening.

11. Positive serology for hepatitis B surface antigen or a history of hepatitis Binfection at screening. Note: Children and adolescents with a history of hepatitis B vaccination without ahistory of hepatitis B infection do not need to be screened for this criterion (assessed via medical history).

12. Obesity as determined by the investigator: For participants <6 years old: BMI >97thpercentile for the corresponding age and gender group; For participants ≥6 yearsold: BMI ≥obesity threshold for the corresponding age and gender group. Note: Refer to "WS/T 423-2022: Growth Standards for Children Under 7" or "WS/T586-2018: Screening for Overweight and Obesity in School-Aged Children andAdolescents."

13. History of mental illness, intellectual disability, substance abuse, or otheradverse conditions (e.g., inability to read, understand, or write) that, in theinvestigator's judgment, may limit participation in the study.

14. Vaccination with an influenza vaccine within six months before screening or duringthe study period. Note: Participants' influenza vaccination history should be carefully reviewedbefore study enrollment (assessed via medical history).

15. Participation in a clinical trial of any investigational drug or device for anyindication within 30 days prior to screening.

16. Intolerance to skin puncture, fainting at the sight of blood or needles, or poorvenous access for blood collection at screening.

17. Other conditions judged by the investigator to be unsuitable for participation inthe study.