Anti-RSV Study in Chinese Patients (ASCENT)

Inclusion Criteria: * Age 18 - 75 years, inclusive. * Confirmed with RSV infection by rapid diagnostic testing. * New onset with documentation of the following symptoms within 72 hours prior to the start of screening: Respiratory symptoms: runny nose, stuffy nose, sneezing, sore throat, earache, cough, shortness of breath; Systemic symptoms: headache, fatigue / lethargy, fever, and muscle and / or joint ache. The patient must have four symptoms of above, and at least one of these must be respiratory symptom in nature. * Able and willing to provide written informed consent and to comply with the study protocol. Exclusion Criteria: * The patient has taken, is taking or needs to take any antiviral medication (e.g. ribavirin, Chinese medicine or herbs with effects of treating respiratory tract infection) within the 72 hours prior to screening. * Awareness of concomitant infections of respiratory viruses (eg, influenza A, B), bacterial or fungal infections, including systemic bacterial or fungal infections within 7 days prior to screening or during the screening period. * Patient frailty was evaluated as "Vulnerable" or worse according to the Clinical Frailty Scale with a score ≥ 4 at screening. * Awareness of having positive results on HBsAg or HCV antibody or HIV (HIV 1 or HIV 2). * Patient with active tuberculosis or is taking antituberculosis treatment. * Patient with severe gastrointestinal disease which could impact drug absorption, eg, vomiting, malabsorption syndrome, or short bowel syndrome caused by necrotizing enterocolitis. * Patient with any congenital heart disease, acute or chronic heart failure, ischemic heart disease, or congenital long QT syndrome, or any clinical manifestation resulting in QT interval prolongation. * Patient with malignant tumor. * Patient has received or is waiting for bone marrow, stem cell or solid organ transplantation. * Patient with any immune-related disease to be treated within 12 months prior to screening. * Patient with clinical laboratoy test values of ≥ 2x the upper limit of normal (ULN) for alanine aminotransferase or aspartate aminotransferase, or \>1x ULN for total bilirubin, or \>1.5xULN for serum creatinine. * Patient with electrolyte disorders, eg, hypokalemia, hypocalcemia, or hypomagnesemia. * Patient with history of drug or alcohol abuse within 12 months prior to screening ("alcohol abuse" definition is \>14 units per week: 1 unit = 10mL Alcohol, or 250mL of 4% beer, or 25 mL of 40% spirit, or 75 mL of 13% wine). * Patient has allergy or hypersensitivity to study medication or its compositions. * Female patient with positive pregnancy test result or is lactating. * Patient with fertility refusing to use medically effective contraceptives during the study or within three months of the end of study. * Patient participated in an investigational drug or device study within 60 days prior to screening. * Patient who in the opinion of the investigator, is deemed as ineligible for the study, including patients who are with active psychiatric disease, or are taking psychiatric medication.