Merck (NYSE:MRK), operating as MSD outside the U.S. and Canada, announced today that the European Commission (EC) has granted marketing authorization for ENFLONSIA™ (clesrovimab).
The approval marks a significant advancement in pediatric preventative care, as ENFLONSIA is now authorized to prevent respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants entering their first RSV season.
RSV is a highly contagious virus that remains a leading cause of bronchiolitis and pneumonia in infants, often resulting in hospitalization for both healthy and at-risk children.
Unlike traditional vaccines, ENFLONSIA is a long-acting monoclonal antibody (mAb).
It is designed to provide direct, rapid, and durable protection lasting up to five months—covering a standard RSV season—with the convenience of non-weight-based dosing.
The EC’s decision is underpinned by robust data from the pivotal Phase 2b/3 CLEVER trial and interim results from the Phase 3 SMART trial.
These studies, published in the New England Journal of Medicine in late 2025, demonstrated the safety and efficacy of clesrovimab in both healthy full-term and preterm infants, as well as those at high risk for severe disease.
The authorization covers all 27 European Union member states, plus Iceland, Liechtenstein, and Norway.
While already approved in the United States, Canada, and Switzerland, the timing of ENFLONSIA's availability in specific European markets will depend on local reimbursement procedures and national healthcare policies.