Merck (NYSE: MRK) announced that the European Commission has approved ENFLONSIA (clesrovimab) for preventing respiratory syncytial virus lower respiratory tract disease in newborns and infants during their first RSV season.

ENFLONSIA is a monoclonal antibody designed to provide protection for five months with a single dose, without requiring weight-based dosing adjustments. The approval covers all 27 European Union member states, plus Iceland, Liechtenstein and Norway.

The approval was supported by results from two clinical trials. The Phase 2b/3 CLEVER trial showed ENFLONSIA reduced RSV-associated medically attended lower respiratory infections by 60.4% and RSV-associated hospitalizations by 84.2% compared to placebo over five months. The Phase 3 SMART trial provided additional safety data in high-risk infants.

In the CLEVER trial, 2,412 participants received ENFLONSIA and 1,202 received placebo. The most frequent adverse reactions were injection-site pain (6.5%), injection-site erythema (4.4%), injection-site swelling (3.2%) and rash (2.3%). More than 96% of adverse reactions were mild or moderate.

The drug is contraindicated for infants with hypersensitivity to the active substance or its excipients. Availability timing in individual countries will depend on completing reimbursement procedures.

ENFLONSIA is already approved in the United States, Canada, Switzerland and several other countries. The company stated regulatory filings are underway in additional markets globally.

RSV is a leading cause of infant hospitalization globally and can progress to serious respiratory conditions including bronchiolitis and pneumonia in both healthy and at-risk infants.