This study is a Phase 3 randomized, double-blind, placebo-controlled study to evaluate the safety, efficacy, and immunogenicity of TNM001 in high-risk infants when entering their RSV season. Approximately 201 infants will be randomized in a ratio of 2:1 to receive TNM001 or placebo. All subjects will be followed for 270 days after dosing. This study will be conducted at approximately 20 sites in China.

Inclusion Criteria:

• 1.High risk infants under 1 year of age who are entering their first RSV season at the time of screening.
• 2.Subject's legal representative(s) is(are) able to understand and comply with the requirements and procedures of the protocol,including scheduled visits and sample collection.
• 3.Subject is available to complete the follow-up period.

Exclusion Criteria:

• 1. Any fever (> 38.0°C) or acute illness within 7 days prior to randomization
• 2. History of RSV infection
• 3. Being hospitalized at the time of randomization
• 4. Currently receiving or expected to receive immunosuppressive therapy during the study period.
• 5. Renal impairment or hepatic dysfunction
• 6. Nervous system disease or neuromuscular disease
• 7. Known immunodeficiency including HIV, mother with HIV infection unless the child's infection has been excluded.
• 8. Known allergy history of immunoglobulin products, receipt or expected to receive immunoglobulins or blood products during the study period.
• 9.Receipt of RSV vaccine or mAb
• 10.Receiving blood products before randomization