The primary objectives of this phase 2b/3 double-blind, randomized, placebo-controlled study are to evaluate the efficacy and safety of clesrovimab in healthy pre-term and full-term infants. It is hypothesized that clesrovimab will reduce the incidence of respiratory syncytial virus (RSV)-associated medically attended lower respiratory infection (MALRI) from Days 1 through 150 postdose compared to placebo.



Eligible Ages
Under 1 Year
Eligible Genders
Accepts Healthy Volunteers

Inclusion Criteria

  • Is a healthy male or female who is an early or moderate pre-term infant (≥29 to 34 weeks and 6 days gestational age) or a late pre-term or full-term infant (≥35 weeks gestational age) - For the phase 2b cohort only: Has a chronological age >2 weeks of age up to 1 year and is entering their first RSV season at the time of obtaining documented informed consent. - For the phase 3 cohort only: Has a chronological age from birth up to 1 year and is entering their first RSV season at the time of obtaining documented informed consent. - For participants in South Korea only: Weighs ≥2 kg

Exclusion Criteria

  • Is recommended to receive palivizumab per local guidelines or professional society recommendations. - Has known hypersensitivity to any component of clesrovimab - Has a bleeding disorder contraindicating IM administration - Has had a recent illness with rectal temperature ≥100.5°F (≥38.1°C) or axillary temperature ≥100.0°F (≥37.8°C) within 72 hours predose - Has received any vaccine or monoclonal antibody 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 before first dose administration or while participating in this study

Study Design

Phase 2/Phase 3
Study Type
Intervention Model
Parallel Assignment
Primary Purpose
Double (Participant, Investigator)

Arm Groups

ArmDescriptionAssigned Intervention
Participants receive a single intramuscular (IM) administration of clesrovimab on Day 1.
  • Biological: Clesrovimab
    Clesrovimab solution
    Other names:
    • MK-1654
Placebo Comparator
Participants receive a single IM administration of placebo on Day 1.
  • Drug: Placebo
    Placebo (0.9% sodium chloride [NaCL]) solution

More Details

Active, not recruiting
Merck Sharp & Dohme LLC

Study Contact


Study information shown on this site is derived from ClinicalTrials.gov (a public registry operated by the National Institutes of Health). The listing of studies provided is not certain to be all studies for which you might be eligible. Furthermore, study eligibility requirements can be difficult to understand and may change over time, so it is wise to speak with your medical care provider and individual research study teams when making decisions related to participation.