About ENFLONSIA▼

ENFLONSIA®▼ (Clesrovimab)
Prescribing Information (United Kingdom) [External link]
By clicking the link above you will leave the MSD Connect website and be taken to the emc Pl portal website

Always refer to the full Summary of Product Characteristics before prescribing for up-to-date and complete safety considerations to help minimise the risks associated with the use of ENFLONSIA.

Indication

ENFLONSIA is indicated for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants during their first RSV season.¹

ENFLONSIA should be used in accordance with official recommendations.¹

ENFLONSIA Information Pack

To support in the completion of a formulary application or clinical guideline development.
Please refer to the SmPCs for full details about managing AEs.

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Guidance on the use of ENFLONSIA from Green Book RSV Chapter 27a (June 2026)⁶

To reduce the risk of severe disease, infants born very or extremely prematurely (<32 weeks gestational age) are recommended to receive a dose of a long-acting monoclonal antibody, clesrovimab or nirsevimab^2, during or preceding their first RSV season.

To reduce the risk of severe disease, eligible high-risk infants are recommended to receive RSV monoclonal antibody immunisation seasonally. This should be offered regardless of whether the mother was vaccinated during the pregnancy. 

High Risk due to chronic lung disease (CLD) of prematurity, also known as bronchopulmonary dysplasia (BPD).⁶

Moderate or severe CLD is defined as ‘pre-term infants with compatible x-ray changes who continue to receive supplemental oxygen or respiratory support at 36 weeks postmenstrual age’.

Infants with respiratory diseases who are not necessarily pre-term, but who remain in oxygen at the start of the RSV season are also considered to be a higher risk.  These infants may include those with conditions including: 

• Pulmonary hypoplasia due to congenital diaphragmatic hernia 
• Other congenital lung abnormalities (sometimes also involving congenital heart disease or lung malformation) 
• Interstitial lung disease 
• Those receiving long-term ventilation (LTV) at the onset of the first season 

High risk due to congenital heart disease (CHD)⁶

Preterm infants with haemodynamically significant, acyanotic CHD at the chronological ages at the start of the RSV season and gestational ages at birth. Infants with cyanotic or acyanotic CHD plus significant co-morbidities particularly if multiple organ systems are involved. 

High risk due to Severe Combined Immunodeficiency Syndrome (SCID)⁶

Infants with SCID – the most severe form of inherited deficiency of immunity, who are unable to mount either T-cell responses or produce antibody against infectious agents.

Full eligibility details can be found in the Green Book RSV Chapter 27a (June 2026).

Clesrovimab or nirsevimab² are the recommended first-line immunisations, if available. Palivizumab³ is recommended if neither of the first line products are available.

dose, regardless of weight¹

Delivers antibodies with one dose
The recommended dose is 105 mg administered as a single 0.7 mL IM injection.^1,a,b

Helps provide 5-month protection¹
Based on clinical efficacy data, duration of protection offered by a single dose of ENFLONSIA® could extend through 6 months, however, few events occurred beyond 5 months, limiting interpretation.¹

1 dose to stock with a 36-month shelf life¹
Which may facilitate supply management efficiencies. ENFLONSIA® may be kept at room temperature (20°C – 25°C) for a maximum 48 hours. After removal from the refrigerator, it must be used within 48 hours or discarded.

Vaccines Supply Status

Our wholesale partner Alliance Healthcare is stocked with Enflonsia across all branches and ready for orders. Any early visibility of expected volumes will help ensure stock is positioned appropriately. Hospitals with indicative volumes can contact Alliance Healthcare directly at customerservice@alliance-healthcare.co.uk, including their account details and required units, to support stock availability.

MSD Medicines and Vaccines can be ordered from:
Alliance Healthcare Customer Services  
Telephone: 0330 100 0448 
Email: customerservice@alliance-healthcare.co.uk

References

1. ENFLONSIA. Summary of Product Characteristics. MSD; 2026.
2. Sanofi (2026). Beyfortus 50 mg solution for injection in pre-filled syringe: Summary of Product Characteristics (SmPC). Electronic Medicines Compendium. Available at: https://www.medicines.org.uk/emc/product/101052/smpc (Accessed: 23 June 2026).
3. AstraZeneca UK Limited (2026). Synagis 100 mg/1 mL solution for injection: Summary of Product Characteristics (SmPC). Electronic Medicines Compendium. Accessed: 28 April 2026. Available at: https://www.medicines.org.uk/emc/product/6963/smpc
4. Beyfortus. Summary of Product Characteristics. Sanofi; 2025. 
5. Synagis. Summary of Product Characteristics. AstraZeneca; 2023.
   a. For infants undergoing cardiac surgery with cardiopulmonary bypass during the RSV season, an additional 105 mg dose is recommended as soon as the infant is stable after surgery to ensure adequate serum levels of ENFLONSIA®.¹ 
   b. There were no significant differences in the pharmacokinetics of ENFLONSIA® observed based on patient characteristics such as race or vulnerability to severe RSV disease (i.e., CHD, CLD or <29 weeks gestational age).¹
6. UK Health Security Agency. The Green Book Chapter 27a Respiratory Syncytial Virus. June 2026. Accessed June 2026. Available at: https://assets.publishing.service.gov.uk/media/6a2015a4730aece621f09866/Green_Book_RSV_20260603.pdf

Supporting documentation

ENFLONSIA®▼ (clesrovimab)
Prescribing Information (United Kingdom) [External link]
By clicking the link above you will leave the MSD Connect website and be taken to the emc PI portal website