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ENFLONSIATM (clesrovimab-cfor) showed a consistent safety profile across infant populations1

Adverse reactions reported at an incidence higher than placebo (CLEVER Trial 004)1
Adverse reactionENFLONSIA
(N=2,412)a
(%)		Placebo
(N=1,202)a
(%)
Injection-site erythemab3.8 3.3
Injection-site swellingb2.72.6
Rashc2.31.9

These were the most commonly reported adverse reactions.

aSample size reflects the number of participants included in the safety analysis population.

bOccurring within 5 days post-dose; Solicited on Day 1 through Day 5 post dose using an electronic diary device.

cOccurring within 14 days post-dose; Defined by the following grouped preferred terms: rash, rash erythematous, rash macular, rash papular, rash maculo-papular, rash vesicular, rash exfoliative, dermatitis allergic, drug eruption, and toxic skin eruption.

Most adverse reactions (≥97%) were mild or moderate in severity.

Infants at increased risk of severe RSV LRT disease in the SMART 007 trial entering their first RSV season had a similar safety profile with ENFLONSIA compared to healthy infants in the CLEVER 004 trial1,2

CLEVER 004 study design

Study design (SMART 007 trial):

An international, randomized, partially-blind, palivizumab-controlled, Phase 3 study evaluated the safety (primary endpoint) and efficacy of ENFLONSIA in infants at increased risk of severe RSV disease. Infants ≤1 year of age and entering their first RSV season were included if they were early (<29 weeks gestational age) or moderate preterm infants ( ≥29 to ≤35 weeks gestational age), or had CLD of prematurity or hemodynamically significant CHD of any gestational age. Participants received a single 105 mg IM dose of ENFLONSIA (N=446) followed by a dose of placebo one month later or 3 to 5 monthly doses of 15 mg/kg palivizumab (N=450).2

See clinical data for ENFLONSIA

Frequently asked questions

References:

  1. Zar HJ, Simões EAF, Madhi SA, et al. Clesrovimab for Prevention of RSV Disease in Healthy Infants. N Engl J Med. 2025;393:1292-1303. DOI: 10.1056/NEJMoa2502984
  2. Sinha A, et al. Evaluation of a monoclonal antibody against respiratory syncytial virus, clesrovimab, in infants and children: Comprehensive rationale and study design for the late-stage clinical trials. Contemp Clin Trials. 2025;157:107995. doi: 10.1016/j.cct.2025.107995.
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Indications and Usage

ENFLONSIA is indicated for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants who are born during or entering their first RSV season.

Selected Safety Information

  • Do not administer ENFLONSIA to infants with a history of serious hypersensitivity reactions, including anaphylaxis, to any component of ENFLONSIA.
  • Serious hypersensitivity reactions, including anaphylaxis, have been observed with other human immunoglobulin G1 (IgG1) monoclonal antibodies. If signs or symptoms of a clinically significant hypersensitivity reaction or anaphylaxis occur, initiate appropriate medications and/or supportive therapy.
  • ENFLONSIA may interfere with some immunologically-based RSV diagnostic assays (i.e., rapid antigen tests) as observed in laboratory studies. Confirmation using a reverse transcriptase polymerase chain reaction (RT-PCR) assay is recommended when rapid antigen assay results are negative and clinical observations are consistent with RSV infection.
  • The most common adverse reactions were injection-site erythema (3.8%), injection-site swelling (2.7%), and rash (2.3%).

 

Dosage and Administration

  • The recommended dose is 105 mg administered as a single intramuscular (IM) injection.
  • For neonates and infants born during the RSV season, administer ENFLONSIA once starting from birth. For infants born outside the RSV season, administer ENFLONSIA once prior to the start of their first RSV season considering 5 months duration of protection by ENFLONSIA.
  • For infants undergoing cardiac surgery with cardiopulmonary bypass during or entering their first RSV season, an additional 105 mg dose is recommended as soon as the infant is stable after surgery to ensure adequate clesrovimab-cfor serum levels.

 

Before administering ENFLONSIA, please read the accompanying Prescribing Information. The Patient Information also is available.

Indications and Usage
Selected Safety Information

ENFLONSIA is indicated for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants who are born during or entering their first RSV season.

Selected Safety Information

  • Do not administer ENFLONSIA to infants with a history of serious hypersensitivity reactions, including anaphylaxis, to any component of ENFLONSIA.
  • Serious hypersensitivity reactions, including anaphylaxis, have been observed with other human immunoglobulin G1 (IgG1) monoclonal antibodies. If signs or symptoms of a clinically significant hypersensitivity reaction or anaphylaxis occur, initiate appropriate medications and/or supportive therapy.
  • ENFLONSIA may interfere with some immunologically-based RSV diagnostic assays (i.e., rapid antigen tests) as observed in laboratory studies. Confirmation using a reverse transcriptase polymerase chain reaction (RT-PCR) assay is recommended when rapid antigen assay results are negative and clinical observations are consistent with RSV infection.
  • The most common adverse reactions were injection-site erythema (3.8%), injection-site swelling (2.7%), and rash (2.3%).

 

Dosage and Administration

  • The recommended dose is 105 mg administered as a single intramuscular (IM) injection.
  • For neonates and infants born during the RSV season, administer ENFLONSIA once starting from birth. For infants born outside the RSV season, administer ENFLONSIA once prior to the start of their first RSV season considering 5 months duration of protection by ENFLONSIA.
  • For infants undergoing cardiac surgery with cardiopulmonary bypass during or entering their first RSV season, an additional 105 mg dose is recommended as soon as the infant is stable after surgery to ensure adequate clesrovimab-cfor serum levels.

 

Before administering ENFLONSIA, please read the accompanying Prescribing Information. The Patient Information also is available.