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RSV disease in infants can progress unpredictably, potentially leading to hospitalization1

Infants may develop RSV-associated bronchiolitis and/or pneumonia with the first RSV infection2

~81% of all RSV-associated health care interactions in infants from a 2011-2019 study were outpatient visits for lower respiratory infections3,a

RSV has been the leading cause of hospitalization among infants in the US. The highest rates occurred in the first few months of life and peaked at just 1 month of age in 2015-2020 4-6,b

74% of infants hospitalized with RSV infection had no history of premature birth or chronic comorbid conditions (based on a study conducted from December 2016 through September 2020)5,c

aThe study estimated the annual incidence of RSV infections in a US cohort of privately insured children <5 years of age (N = 6,767,107) between 2011 – 2019. Results were stratified by age. Medical encounters evaluated included inpatient, ICU, outpatient, and emergency department visits.3

bBased on two prospective, population-based, surveillance studies of RSV-associated hospitalizations in US children <5 years of age at seven pediatric medical centers, utilizing NVSN data from 2015–2016 and 2016–2020.4,5

cBased on a prospective surveillance study in RSV-positive children <5 years old (n=4,243) with acute respiratory illness conducted from December 2016 through September 2020 at seven pediatric medical centers. Of these, 2,813 were infants <12 months of age.5

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Frequently asked questions

References:

  1. Clinical overview of RSV. Centers for Disease Control and Prevention. August 18, 2025. Accessed October 27, 2025. https://www.cdc.gov/rsv/hcp/clinical-overview/index.html
  2. Respiratory syncytial virus. In: Kimberlin DW, Banerjee R, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book: 2024-2027 Report of the Committee on Infectious Diseases. 33rd ed. American Academy of Pediatrics. 2024;713-721.
  3. Nduaguba SO, Tran PT, Shih R, et al. Respiratory syncytial virus incidence in young children in the United States: impact of methodologies and patient characteristics. Influenza Other Respir Viruses. 2025;19(4):e70094. doi:10.1111/irv.70094
  4. Curns AT, Rha B, Lively JY, et al. Respiratory syncytial virus-associated hospitalizations among children <5 years old: 2016 to 2020. Pediatrics. 2024;153(3):e2023062574. doi:10.1542/peds.2023-062574
  5. Rha B, Curns AT, Lively JY, et al. Respiratory syncytial virus-associated hospitalizations among young children: 2015-2016. Pediatrics. 2020;146(1):e20193611. doi:10.1542/peds.2019-3611
  6. RSV in infants and young children. Centers for Disease Control and Prevention. August 30, 2024. Accessed February 27, 2025. https://www.cdc.gov/rsv/infants-young-children/index.html
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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.