The purpose of this clinical trial is to evaluate the safety, tolerability and pharmacokinetics (PK) profile of TNM001 injection in healthy preterm and term infants. The main questions it aims to answer are:

• the safety and tolerability of TNM001 injection
• the pharmacokinetic (PK) profile of TNM001

This phase Ib/IIa study is designed to assess the safety, tolerability, and pharmacokinetics (PK) profile TNM001 in healthy preterm and term infants. This study will also compare the incidence of Respiratory Syncytial Virus（RSV） infection between different doses of TNM001 and placebo, which will be used to select the dose to be studied in the later phase of clinical trials of TNM001. Approximately 30 subjects will be randomized and will be dosed once on Day 1 and followed up until Day 151. Around 6 investigational study centres participate in the study.

Key Inclusion Criteria:

1. Healthy preterm infants and term infants within 1 year old of age
2. Infants who are in the first RSV infection season at the time of randomization

Key Exclusion Criteria:

1. Any fever or acute illness within 7 days prior to dosing
2. LRTI prior to randomization
3. Received any anti-RSV monoclonal antibody or RSV vaccine
4. Any other circumstances that, in the opinion of the investigator, may interfere with the assessment of the study drug or the interpretation of the study results
5. The subject is a child of the investigator or his/her subordinate study personnel or relatives or sponsor staff