TLDR
- Merck stock climbs 0.65% to $147.90 after positive EU opinion on ENFLONSIA.
- EU advisers back ENFLONSIA use for high-risk children through a second RSV season.
- European Commission decision on Merck’s expanded RSV treatment is due in two months.
- Phase 3 SMART trial data support Merck’s bid to expand RSV prevention in Europe.
- FDA sets March 22, 2027, decision date for ENFLONSIA’s wider US indication.
Merck & Co. (MRK) stock rose 0.65% to $147.90, gaining $0.95 as European regulators backed an expanded indication for ENFLONSIA. The shares recovered from intraday lows near $145.50 as buying activity strengthened during the session. Meanwhile, the recommendation brings Merck closer to expanding RSV prevention for high-risk children across Europe.
European Regulators Support Merck’s RSV Drug Expansion
The European Medicines Agency’s Committee for Medicinal Products for Human Use issued a positive opinion on Merck’s ENFLONSIA treatment. The recommendation covers children under 24 months who face increased risks of severe respiratory syncytial virus infections. The proposed expansion would extend protection through their second RSV season.
The European Commission will now review the recommendation before deciding whether to authorize the expanded indication. Merck expects a final decision within two months, covering the European Union, Iceland, Liechtenstein, and Norway. The proposed approval would address children with underlying conditions that increase their vulnerability to serious respiratory illness.
These conditions include chronic lung disease, congenital heart disease, and certain complications linked to premature birth. Such children can develop severe RSV infections, including pneumonia and bronchiolitis, during their second RSV season. Merck aims to extend preventive treatment beyond the first season for eligible children.
Phase 3 Trial Supports ENFLONSIA Regulatory Expansion
Merck supported its European application with findings from the Phase 3 SMART clinical trial. The study assessed ENFLONSIA’s safety, effectiveness, and drug exposure among children facing elevated risks of severe RSV disease. Researchers compared ENFLONSIA with palivizumab during the first RSV season and evaluated eligible children during the second season.
During the first season, researchers assigned 502 participants to ENFLONSIA and 501 to monthly palivizumab injections. Meanwhile, 276 eligible children received an additional 210 mg ENFLONSIA dose during their second RSV season. Most second-season participants had chronic lung disease or congenital heart disease, reflecting the targeted population.
Merck presented trial findings at the February 2026 RSVVW conference and published additional results in medical journals. The company previously secured FDA approval for ENFLONSIA in June 2025 for infants entering their first RSV season. Subsequently, the European Commission granted approval in April 2026, extending the treatment’s reach across European markets.
Merck Advances RSV Treatment Across Global Markets
ENFLONSIA currently holds approvals in more than 55 countries, including the United States, Canada, China, and Japan. Unlike weight-based alternatives, the treatment uses a standard 105 mg dose for infants during their first RSV season. Furthermore, its extended half-life monoclonal antibody design provides protection for approximately five months.
Merck also seeks expanded authorization in the United States for high-risk children entering their second RSV season. The FDA accepted the supplemental application and set March 22, 2027, as its target decision date. Meanwhile, Merck continues pursuing additional regulatory approvals across international markets.
The latest European recommendation marks another regulatory development for Merck’s growing RSV prevention portfolio. However, the expanded European indication still requires formal authorization from the European Commission before implementation. Merck shares ended the reported session higher, reflecting a 0.65% gain alongside the regulatory announcement.
