To evaluate the safety, efficacy, pharmacokinetic (PK) characteristics and antiviral activity of different doses of Deuterium Hydrobromide for suspension in the treatment of respiratory syncytial virus infection in infants.

This trial is a randomized, double-blind, placebo-controlled, dose-ascending trial, and the subjects are infants infected with RSV from 1 to 24 months.

It is estimated that 60 subjects will be included and divided into low-dose group (15 mg/kg，BID), middle-dose group (20 mg/kg,BID) and high-dose group (20 mg/kg,TID), with 20 cases in each group, and they will be randomly assigned to the experimental drug group and the placebo group according to the ratio of 3: 1.

Inclusion Criteria:

1. Male or female infants ≥1 month and ≤24 months；
2. Diagnosis of RSV infection by antigen detection or nucleic acid within 36 hours preceding initial dosing；
3. Onset of RSV infection symptoms should be ≤ 5 days；
4. Patient must weigh ≥ 2.5 kg and ≤ 20 kg at screening；
5. Patient must have a Wang Respiratory Score ≥ 5;
6. Patient who are hospitalized or in emergency/outpatient department and are expected to be hospitalized;
7. The parent/legal guardian must have provided written informed consent for the patient to participate.

Exclusion Criteria:

1. Patients who are less than 12 months old and whose head circumference is not within the normal range corresponding to their age and gender at the time of screening;
2. Patients who have received prohibited used drugs (except external preparations) specified in the protocol for a specified time.
3. Requires vasopressors or inotropic support at the time of enrollment;
4. Patients with known SARS-CoV-2 infection, influenza virus infection, mycoplasma infection or bacterial infection；
5. Patients with hypercapnia (Except for patients who have recovered at the time of screening);
6. Chronic or persistent feeding difficulties;
7. Concurrent gastrointestinal conditions that could seriously, in the opinion of the investigator, prejudice absorption of the Investigational Medicinal Product;
8. Symptomatic because of inborn errors of metabolism;
9. Bronchopulmonary dysplasia requiring assisted ventilationor with clinically significant congenital respiratory abnormalities, except for the result of RSV infection;
10. Patients with congenital heart disease (CHD) with significant hemodynamic changes, except simple CHD (such as patent ductus arteriosus, atrial septal defect or ventricular septal defect without hemodynamic influence).
11. Clinical evidence of hepatic decompensation
12. Renal failure including renal anomalies likely to be associated with renal insufficiency;
13. Patient is known to be HIV-positive (or the mother, if the potential patient is a child aged <6 months);
14. Suspected or known to have congenital acquired immunodeficiency;
15. A history of epilepsy or seizures;
16. A history of high allergies;
17. Any active or uncontrolled respiratory, cardiac, hepatic, central nervous system, or renal disease unrelated to RSV infection at baseline or any other medical condition that in the opinion of the investigator renders the patient unsuitable for enrollment;
18. Participation in an investigational drug or device study within 30 days prior to the date of screening;
19. Failure to satisfy the investigator of fitness to participate for any other reason.