Merck’s Phase 3 Trial Shows ENFLONSIA Extends Five-Month RSV Protection in High-Risk Children
Merck’s Phase 3 SMART trial found that second-season administration of ENFLONSIA in infants and children at increased risk produced serum concentrations comparable to healthy infants, supporting extended RSV protection up to five months. Safety remained consistent with first-season findings, with no serious adverse events reported.
1. Positive Phase 3 SMART Trial Findings
On February 19, Merck announced that the Phase 3 SMART trial evaluating ENFLONSIA in infants and children at increased risk for severe RSV during their second season produced serum concentrations comparable to healthy infants from pivotal studies, supporting exposure for extended protection.
2. Consistent Safety Profile
Safety results remained consistent with first-season data, reporting common side effects such as irritability, somnolence and injection-site reactions, with no drug-related serious adverse events observed.
3. Regulatory Expansion Plans
Following FDA approval in June 2025 for first-season use, Merck intends to submit these second-season trial results to US and international regulators to seek an expanded indication for high-risk children entering their second RSV season.