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Clinical data for ENFLONSIATM (clesrovimab-cfor)

Proven to help provide robust RSV LRT disease protection

See study design

Efficacy endpoints evaluated required an RSV-positive RT-PCR NP sample.

n = Number of participants eligible in the full analysis set population.

aEfficacy for MALRI (requiring ≥1 indicator of LRI or severity) and hospitalization based on relative risk reduction against placebo adjusted for hemisphere at randomization, gestational age group, and age group at randomization.

bEstimate and 95% CI of efficacy were estimated from the modified Poisson regression with robust variance method.

cMedically attended included all health care provider visits in settings such as outpatient clinic, clinical study site, emergency department, urgent care center, and/or hospital.

Study design (CLEVER 004 trial): The efficacy and safety profile of ENFLONSIA was evaluated in an international, randomized, double-blind, Phase 2b/3 study of healthy early and moderate preterm (≥29 to <35 weeks gestational age) and late preterm and full-term (≥35 weeks gestational age) infants ≤1 year of age entering their first RSV season. Participants were randomized 2:1 to receive a single 105 mg dose of ENFLONSIA or saline placebo by IM injection.1

CI, confidence interval; ICU, intensive care unit; IM, intramuscular; LRI, lower respiratory infection; LRT, lower respiratory tract; MALRI, medically attended lower respiratory infection; NP, nasopharyngeal; NVSN, New Vaccine Surveillance Network; RT-PCR, reverse transcriptase polymerase chain reaction.

See safety profile

Additional data from CLEVER trial1

See study limitations

Efficacy endpoints evaluated required an RSV-positive RT-PCR NP sample.2

n=Number of participants eligible for inclusion in the full analysis set population.

dResults presented reflect those within CLEVER 004 Clinical Study. The denominators of these results, which reflect total evaluated participants for the exploratory endpoints, differ slightly from the denominators reflected in the US Prescribing Information, which inform the primary and key secondary endpoints.1

eEstimate and 95% CI of observed efficacy were estimated from the modified Poisson regression with robust variance method.

Study limitations:

  • No formal statistical testing was planned for the prespecified exploratory endpoints
  • No conclusions can be drawn from these results and they should be interpreted with caution

CI, confidence interval; ICU, intensive care unit; IM, intramuscular; LRI, lower respiratory infection; LRT, lower respiratory tract; MALRI, medically attended lower respiratory infection; NP, nasopharyngeal; NVSN, New Vaccine Surveillance Network; RT-PCR, reverse transcriptase polymerase chain reaction.

See safety profile

ENFLONSIA safety profile

ENFLONSIA dosing & administration

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. Zar HJ, Simões EAF, Madhi SA, et al. Supplementary appendix to: Clesrovimab for prevention of RSV disease in healthy infants. N Engl J Med. 2025;393(13):1292-1303. doi:10.1056/NEJMoa2502984
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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.