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ENFLONSIATM (clesrovimab-cfor) is designed to rapidly provide antibodies

to help protect infants entering their first RSV season

RSV infects cells along the respiratory tract from the nose to the lungs, causing a wide spectrum of respiratory disease, including lower respiratory tract infection1

Nasal passage

How ENFLONSIA™ (clesrovimab-cfor) Interacts with RSV in the Nasal Lining Fluid

ENFLONSIA has been detected in the lining fluid of the nasal mucosal cells in adults—an important point of viral entry into the body.2,3

RSV-neutralizing antibody titers in serum were estimated to be ~7x higher than baseline levels at 4 hours following administration

RSV membrane: a closer look

ENFLONSIA™ (clesrovimab-cfor) Binds to Site IV After Administration
  • Binds to antigenic site IV (highly conserved in 99.8% of strains)a
  • Fully human mAb modified for extended serum half-lifeb

aIn sequences reported in GenBank database (accessed 4/2024).

bModified with a triple amino acid substitution (YTE) in the Fc region.

F protein, fusion protein; IM, intramuscular; RSV, respiratory syncytial virus; Fc, Fragment crystallizable.

What is RSV?

Order ENFLONSIA now

References:

  1. Respiratory syncytial virus (RSV). World Health Organization. Published December 19, 2025. Accessed January 6, 2025. https://www.who.int/news-room/fact-sheets/detail/respiratory-syncytial-virus-(rsv)#
  2. How RSV spreads. Centers for Disease Control and Prevention. July 8, 2025. Accessed July 24, 2025. https://www.cdc.gov/rsv/causes/
  3. Phuah JY, Maas BM, Tang A, et al. Quantification of clesrovimab, an investigational, half-life extended, anti-respiratory syncytial virus protein F human monoclonal antibody in the nasal epithelial lining fluid of healthy adults. Biomed Pharmacother. 2023;169:115851. doi:10.1016/j.biopha.2023.115851
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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.