Merck announced that the European Commission (EC) has approved ENFLONSIA (clesrovimab) for the prevention of Respiratory Syncytial Virus (RSV) lower respiratory tract disease in neonates (newborns) and infants during their first RSV season. ENFLONSIA is contraindicated for infants with hypersensitivity to the active substance or any of its excipients.

ENFLONSIA is a preventive, long-acting monoclonal antibody (mAb) designed to provide direct, rapid and durable protection through 5 months, a typical RSV season, with non-weight-based dosing. The EC approval authorises the marketing of ENFLONSIA in all 27 European Union (EU) member states, as well as Iceland, Liechtenstein and Norway. The timing for availability of ENFLONSIA in individual countries will vary by country and depend on multiple factors, including the completion of reimbursement procedures.

“RSV can progress to severe conditions like bronchiolitis and pneumonia in both healthy and at-risk infants and is among the leading causes of infant hospitalisation globally,” said Dr. Paolo Manzoni, Head of Maternal–Infant Medicine, University of Torino Hospital Degli Infermi, Ponderano, Italy, and an investigator for the SMART clinical trial. “The approval of ENFLONSIA in Europe represents an important public health achievement. Backed by strong clinical data from the CLEVER and SMART trials showing significant reductions in RSV disease incidence and RSV-associated hospitalisations, paired with dosing convenience, ENFLONSIA is a valuable new option with potential to help alleviate the burden of RSV on infants, families and health care systems.”

“The European Commission approval of ENFLONSIA marks a significant milestone in our journey to enable broad access and help reduce the burden of RSV disease on infants around the world,” said Dr. Macaya Douoguih, Vice President, Therapeutic Area Head, Global Clinical Development, Merck Research Laboratories. “We are proud to bring ENFLONSIA to infants in Europe and look forward to equipping families and health care providers with this important new preventive option to help address this widespread and potentially serious disease."

The EC approval is supported by results from the phase-IIb/III CLEVER trial (MK-1654-004; NCT04767373), which evaluated the safety and efficacy of a single dose of ENFLONSIA administered to preterm and full-term infants (birth to 1 year of age), as well as interim data from RSV season one of the phase-III SMART trial evaluating the safety, efficacy and pharmacokinetics of ENFLONSIA versus palivizumab in infants at increased risk for severe RSV disease. Clinical data from the CLEVER and SMART trials were published in the New England Journal of Medicine in September 2025.

ENFLONSIA is approved in the US, Canada, Switzerland and several other countries for use in infants during their first RSV season, and regulatory filings are underway in additional markets globally.