Merck Secures EU Nod for RSV Antibody Enflonsia in Infants
Merck MRK announced that the European Commission (EC) has approved Enflonsia (clesrovimab) for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in newborns and infants during their first RSV season.
Enflonsia is contraindicated for infants with hypersensitivity to the active substance or any of its other components.
Following the latest nod, Enflonsia became the first and only RSV preventive option for administration to infants without the need for weight-based dosing in the European Union ("EU").
The nod in the EU was based on data from the pivotal phase IIb/III CLEVER study, which evaluated the safety and efficacy of a single dose of Enflonsia administered to preterm and full-term infants, as well as interim data from RSV season 1 of the Phase 3 SMART study, evaluating the safety, efficacy and pharmacokinetics of Enflonsia versus palivizumab in infants who stand at increased risk for severe RSV disease.
Merck’s Stock Performance
Year to date, shares of Merck have rallied 13.1% against the industry’s decline of 2.8%.
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Last June, the FDA approved Enflonsia for the prevention of RSV in newborns and infants born during or entering their first RSV season.
Enflonsia sales in the United States were $21 million in the fourth quarter of 2025 compared with $79 million in the third quarter of 2025. A lower-than-expected infant immunization rate and high market inventory levels hurt sales in the fourth quarter.
As Merck prepares to report its first-quarter 2026 results on April 30, it remains to be seen how Enflonsia performs in the quarter.
Other RSV Antibodies/Vaccines Available in the Market
Enflonsia faces competition from AstraZenecaAZN/Sanofi’s SNY RSV antibody Beyfortus, which is approved for a similar indication.
In 2025, the AZN/SNY antibody recorded sales worth €1.8 billion, up 9.5% on a year-over-year basis, reflecting strong demand.
Besides antibodies, some vaccines have been approved for preventing RSV in certain patients in the United States. These include Pfizer’s Abrysvo, GSK’s Arexvy and Moderna’s mRESVIA. Notably, most of these marketed RSV vaccines are approved for use in older adults aged 60 years and above.
MRK’s Zacks Rank
Merck currently carries a Zacks Rank #3 (Hold). You can see the complete list of today’s Zacks #1 Rank (Strong Buy) stocks here.
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