Safety, Tolerability, and Pharmacokinetics of Clesrovimab (MK-1654) in Infants (MK-1654-002)

The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics, and incidence of anti-drug antibodies (ADAs) of single ascending doses of clesrovimab in healthy pre-term (born at 29 to 35 weeks gestational age) and full-term (born at \>35 weeks gestational age) infants. Participants will be randomized into 1 of 4 dose escalation panels (Panels A to D); an additional panel (Panel E) of full-term infants will receive the same dose as Panel D. Key safety and tolerability variables will be reviewed after each dose panel prior to administering the next-highest dose.

Participants in Dose Panels A, B, C, D1, and E1 will be followed for up to 365 days. After protocol Amendment 4 (AM4), participants in Dose Panels D2 and E2 will be followed for up to 545 days.

Eligibility Criteria:
Inclusion Criteria:

* is healthy, based on screening safety laboratory, medical history, and physical examination results
* is a pre-term infant (born at 29 weeks to 35 weeks gestational age \[inclusive\]) or a full-term infant (born at over 35 weeks gestational age), as confirmed in medical records
* weighs ≥2 kg at screening

Exclusion Criteria:

* has been recommended to receive palivizumab per local standard of care
* has ≥1 documented out-of-range safety laboratory results (adjusted for age) at the time of screening
* has a known hypersensitivity to any component of the respiratory syncytial virus (RSV) monoclonal antibody
* has a history of congenital or acquired immunodeficiency (e.g., splenomegaly)
* has documented human immunodeficiency virus (HIV) infection, hepatitis B (HBsAg positive), or hepatitis C (HCV ribonucleic acid \[RNA\] positive)
* has known history of functional or anatomic asplenia
* has a diagnosis of failure to thrive within 14 days of screening
* has known or history of a coagulation disorder contraindicating intramuscular injection
* has received or is expected to receive blood products (except irradiated platelets) within 3 months prior to enrollment
* has prior known documented RSV infection
* has hemodynamically significant congenital heart disease
* has chronic lung disease of prematurity requiring ongoing medical therapy
* has a history or current evidence of any condition, therapy, lab abnormality or other circumstance that, in the opinion of the investigator, might expose the participant to undue risk by participating in the study, confound the results of the study, or interfere with the participant's participation for the full duration of the study
* has any history of malignancy prior to randomization
* if any of the following apply, the Day 1 visit may be rescheduled for a time when these criteria are not met:
* has had a recent febrile illness (rectal temperature 38.1°C \[100.5°F\] or higher or axillary temperature 37.8°C \[100.0°F\] or higher) within 72 hours pre-dose
* is not up-to-date on required vaccinations per local pediatric vaccine schedule at time of screening
* has received inactivated or component vaccines (eg, influenza, hepatitis B) less than 14 days pre-dose
* has received live, attenuated, non-study licensed pediatric vaccines (e.g., Bacillus Calmette-Guerin vaccine) less than 30 days pre-dose
* has received any prior vaccine or monoclonal antibody (mAb) for the prevention of RSV
* is currently participating in or has participated in an interventional clinical study with an investigational compound or device at any time prior to first dose administration or while participating in this current study (participants enrolled in observational studies may be included and will be reviewed on a case-by-case basis for approval by the Sponsor)
* has enrolled previously in this study and been discontinued
* participant's mother participated in a RSV vaccine clinical study while pregnant and participant is ≤3 months of chronological age
* is unable to provide blood sample at screening
* cannot be adequately followed for safety according to the protocol plan
* has a parent/legally acceptable representative who is unlikely to adhere to study procedures, keep appointments, or is planning to relocate during the study
* is, or has, an immediate family member (eg, spouse, parent/guardian, sibling, or child) who is directly involved with the study at the site or with the Sponsor