EU Approves Merck’s ENFLONSIA to Prevent Infant RSV

The European Commission has granted approval to ENFLONSIA, a preventive therapy developed by Merck & Co., for protecting newborns and infants against respiratory syncytial virus (RSV). The decision marks a significant step in addressing a leading cause of infant hospitalizations worldwide.

ENFLONSIA (clesrovimab) is a long-acting monoclonal antibody designed to provide rapid and sustained protection against RSV-related lower respiratory tract disease. It is intended for use in neonates and infants during their first RSV season, offering protection for up to five months with a single, non-weight-based dose. The approval covers all 27 European Union member states, along with Iceland, Liechtenstein, and Norway, although availability will depend on country-specific reimbursement and rollout processes.

RSV is a common but potentially serious virus that can lead to conditions such as bronchiolitis and pneumonia, particularly in infants. It remains one of the primary drivers of pediatric hospital admissions globally, placing a considerable burden on healthcare systems and families. Health experts have long emphasized the need for effective preventive options, especially for infants in their first year of life.

The European Commission’s decision is supported by strong clinical evidence from late-stage trials. Data from the Phase 2b/3 CLEVER study demonstrated that a single dose of ENFLONSIA significantly reduced the incidence of RSV disease in both preterm and full-term infants. Additional support came from interim results of the Phase 3 SMART trial, which evaluated the therapy against palivizumab, a currently used preventive treatment for high-risk infants. These studies also highlighted reductions in RSV-related hospitalizations and confirmed the therapy’s safety profile.

Clinical findings from both trials were published in September 2025 in the New England Journal of Medicine, reinforcing confidence in the treatment’s efficacy and real-world potential.

Medical experts have welcomed the approval, noting that ENFLONSIA could play a key role in reducing RSV-related complications. Its simplified dosing regimen is also expected to improve accessibility and compliance compared to existing preventive options.

ENFLONSIA has already been approved in several countries, including the United States, Canada, and Switzerland, with additional regulatory reviews ongoing globally. Merck continues to expand its RSV prevention strategy, aiming to provide broader protection against the virus and reduce its global impact on infant health.

The approval represents a major milestone for pediatric infectious disease prevention, offering a new tool to help safeguard vulnerable infants during a critical period of early development.