Inclusion Criteria:
* During screening, infants within 1 year of age, including premature infants (gestational age ≥29 to \<35 weeks) and full-term infants (gestational age ≥35 weeks), with underlying diseases but no other risk factors, are allowed to participate in the trial;
* Infants with a body weight ≥3 kg at screening;
* Infants who are entering their first RSV infection season at screening;
* Parents/legal guardians of trial participants have signed the informed consent form;
* Parents/legal guardians of trial participants are able to understand and comply with the requirements and procedures of the protocol, including scheduled center visits, telephone interviews, and blood sample collection;
* Participants can complete the follow-up period, which is approximately 1 year after the administration of the study drug.
Exclusion Criteria:
* Any fever (≥37.5°C, axillary temperature) or acute illness (defined as the presence of moderate or severe symptoms or signs) occurring within 7 days prior to drug administration;
* Having experienced Lower Respiratory Tract Infections (LRTI) within the previous 7 days prior to randomization, or having active LRTI at the time of randomization;
* Individuals with chronic eczema or urticaria, or those with an allergic constitution who are allergic to multiple drugs, or those with a known history of allergy to immunoglobulin products, blood products, other exogenous proteins, or any components of this product;
* Had a history of RSV infection before randomization, or had active RSV infection at the time of randomization;
* Those who have received non-oral inactivated vaccines or component vaccines within 7 days before administration;
* Having received a non-oral live attenuated vaccine within 30 days prior to drug administration;
* Participants who have received any medication within 7 days prior to drug administration, except for: a) various vitamins and iron supplements; b) systemic over-the-counter medications (such as analgesics) for common pediatric symptoms, which may be used occasionally, as determined by the investigator;
* Participants with autoimmune diseases who are currently receiving, or are expected to receive according to the investigator's judgment, immunosuppressive therapy (including steroids, excluding topical steroids) during the trial period;
* Have previously used or are expected to receive blood products or immunoglobulin products during the trial period;
* Known renal dysfunction or liver dysfunction;
* Known to have chronic lung disease (CLD)/bronchopulmonary dysplasia;
* Congenital respiratory abnormalities with clinical significance;
* Suffering from congenital heart disease (CHD) accompanied by significant hemodynamic changes;
* Suffering from chronic epilepsy or progressive or unstable neurological disorders;
* Those who have previously experienced or are suspected to have experienced life-threatening acute events, and are still deemed unsuitable for participating in clinical trials by the researchers;
* Known immune deficiency, including infection with human immunodeficiency virus (HIV);
* The mother is infected with HIV (unless it has been proven that the trial participant is not infected);
* The mother received the RSV vaccine during pregnancy;
* Have received any investigational drugs or participated in any intervention studies;
* Any other circumstances that the researcher believes may interfere with the evaluation of the study drug or the interpretation of the study results;
* The participants are the children of the researchers, their subordinate researchers, relatives, or staff members of the sponsor.
