Inclusion Criteria:
Participants must meet all of the following criteria to be eligible for enrollment in this study:
* 1\. Aged 18 to 85 years (inclusive), male or female.
* 2\. Body mass index (BMI) between 18 kg/m² and 35 kg/m² (inclusive).
* 3\. Presence of at least one of the following newly occurring respiratory tract infection symptoms or systemic symptoms (total symptom score ≥3 points); or worsening of pre-existing respiratory symptoms (total symptom score ≥3 points and an increase of at least 2 points from baseline):
* Respiratory symptoms: cough, sore throat, nasal congestion, wheezing (whistling sound during breathing), cough with phlegm, and shortness of breath;
* Systemic symptoms: headache, feeling feverish, body aches, fatigue, neck pain, sleep disturbance, and loss of appetite.
* 4\. Onset of RSV infection symptoms or worsening of pre-existing non-RSV infection symptoms meeting criterion 3 at enrollment, occurring within ≤72 hours prior to the first dose.
* 5\. Diagnosis of RSV infection confirmed by antigen or RT-PCR testing within 36 hours prior to the first dose.
* 6\. Participants and their partners agree to have no pregnancy plan and no sperm/egg donation plan from screening until 3 months after the last administration of the investigational product, and voluntarily agree to use effective contraceptive measures.
* 7\. Participants voluntarily participate in the study and sign the informed consent form (ICF).
Exclusion Criteria:
Participants meeting any of the following criteria will be excluded from this study:
* 1\. Patients with definite diagnosis of pneumonia.
* 2\. Known concomitant acute respiratory infection other than RSV (e.g., influenza, COVID-19, mycoplasma) within 3 days prior to screening.
* 3\. Known severe gastrointestinal diseases affecting absorption of the study drug (e.g., severe persistent vomiting, malabsorption syndrome, short-bowel syndrome due to necrotizing enterocolitis, etc.).
* 4\. Any of the following cardiovascular or cerebrovascular events within 6 months prior to screening: unstable angina requiring hospitalization, myocardial infarction, coronary artery bypass grafting, percutaneous coronary intervention (diagnostic angiography and PCI performed \>3 months ago are permitted), heart failure (NYHA Class III or IV), atrial or ventricular arrhythmias requiring hospitalization (e.g., atrial fibrillation, ventricular tachycardia, etc.), pacemaker or defibrillator implantation, transient ischemic attack, or cerebrovascular event (e.g., stroke); or planned revascularization procedures (e.g., coronary artery bypass surgery) during the study.
* 5\. Awaiting or having received bone marrow transplantation, stem cell transplantation, or solid organ transplantation within 1 year prior to screening.
* 6\. History of current or previous malignancy (except for malignancies that are well controlled and do not affect the study progress or efficacy evaluation, such as completely resected basal cell carcinoma of the skin, carcinoma in situ of the cervix, or thyroid cancer).
* 7\. Severe or uncontrolled concomitant diseases, including but not limited to autoimmune, cardiovascular, hematologic, respiratory, hepatobiliary, gastrointestinal, endocrine, urinary, psychiatric, or neurologic disorders, which, in the investigator's judgment, would increase the risk to the participant if enrolled.
* 8\. History of drug abuse, drug addiction, and/or alcohol abuse within 6 months prior to screening (alcohol abuse defined as weekly consumption of \>14 units of alcohol: 1 unit = 360 mL beer, or 45 mL of 40% spirits, or 150 mL wine).
* 9\. Known allergy to the study drug or its components.
* 10\. Use of medications that may affect the efficacy or mechanism of the study drug within 5 half-lives prior to randomization (per the drug label; if half-life is unclear, within 7 days prior to randomization) or planned use during the study, including but not limited to: systemic antivirals (ribavirin, interferons, etc., excluding nucleos(t)ide analogues for hepatitis B and direct-acting antivirals for hepatitis C), inhaled corticosteroids (except for COPD and asthma patients on stable prior inhaled corticosteroid therapy), immunomodulators, and Chinese herbal medicines with antiviral activity, etc.
* 11\. Participation in another clinical trial within 3 months (or 5 half-lives, whichever is longer) prior to screening (except for those not receiving any intervention).
* 12\. At screening, clinical laboratory values meeting the following criteria: ALT ≥3×ULN or AST ≥3×ULN; serum TBIL ≥1.5×ULN.
* 13\. Positive HIV-Ab test result.
* 14\. Positive pregnancy test or breastfeeding female patients.
* 15\. Patients who, after instruction by the investigator, are still unable to complete the Respiratory Infection Severity and Impact Questionnaire.
* 16\. Any other condition that, in the investigator's judgment, makes the participant unsuitable for participation in the study.
Additional exclusion criteria for COPD participants:
* 17\. Acute exacerbation of COPD within 6 weeks prior to screening requiring treatment with systemic corticosteroids and/or antibiotics, or emergency room visit or hospitalization.
* 18\. More than 3 acute exacerbations of COPD in the past 12 months.
* 19\. Resting pulse oximetry (SpO₂) reading \<88% at screening, or long-term oxygen therapy (i.e., prescribed for ≥12 hours per day).
