EU panel backs Merck's RSV drug for a second season of protection

Merck & Co.'s RSV shot ENFLONSIA cleared a key European hurdle. The European Medicines Agency's Committee for Medicinal Products for Human Use handed the treatment a positive opinion, backing an expanded label for children under 24 months at higher risk of severe respiratory syncytial virus. The proposed expansion would carry protection into a second RSV season.

The European Commission now reviews the recommendation and decides whether to authorize the wider use. Merck expects a final call within two months, with the decision covering the European Union, Iceland, Liechtenstein and Norway. The label would target kids with chronic lung disease, congenital heart disease or complications tied to premature birth — the children most likely to develop pneumonia or bronchiolitis in that second season.

Merck's European filing leaned on its Phase 3 SMART trial. In the first RSV season, 502 participants got ENFLONSIA while 501 received monthly palivizumab injections; in the second season, 276 eligible children picked up an extra 210 mg dose of ENFLONSIA. Most of those second-season participants had chronic lung disease or congenital heart disease, matching the population the company is chasing.

The company presented the trial findings at the February 2026 RSVVW conference and published further results in medical journals. ENFLONSIA already won FDA approval in June 2025 for infants entering their first RSV season, followed by a European Commission green light in April 2026. It holds approvals in more than 55 countries, including the US, Canada, China and Japan.

Unlike weight-based alternatives, ENFLONSIA uses a standard 105 mg dose for infants in their first RSV season, and its extended half-life monoclonal antibody design protects for roughly five months. Merck is pushing for a matching expansion in the US too: the FDA accepted its supplemental application and set March 22, 2027 as the target decision date. Investors took the news in stride — MRK added $0.95, a 0.65% gain, and finished the session at $147.90 after climbing back from lows near $145.50.