FDA approves Merck’s RSV prevention drug for infants

Published 09/06/2025, 20:18
FDA approves Merck’s RSV prevention drug for infants

RAHWAY, N.J. - Merck & Co. Inc. (NYSE:MRK) announced today that the U.S. Food and Drug Administration (FDA) has approved its monoclonal antibody, ENFLONSIA™ (clesrovimab-cfor), for the prevention of respiratory syncytial virus (RSV) in newborns and infants during their first RSV season. This approval marks a significant advancement in the fight against the leading cause of infant hospitalization in the United States.

ENFLONSIA is designed to provide direct, rapid, and durable protection for up to five months, which typically covers the duration of an RSV season. The approval is based on the results of the Phase 2b/3 CLEVER trial, which showed that ENFLONSIA reduced the incidence of RSV-associated medically attended lower respiratory infections by 60.5% and RSV-associated hospitalizations by 84.3% compared to placebo.

The drug’s efficacy and safety were also supported by the Phase 3 SMART trial, which compared ENFLONSIA to palivizumab in infants at increased risk for severe RSV disease. The results demonstrated that ENFLONSIA’s safety profile was generally comparable to palivizumab. This development adds to Merck’s robust portfolio, which generates annual revenues of $63.92 billion with an impressive gross profit margin of 77.07%.

ENFLONSIA is administered as a single 105 mg dose, regardless of the infant’s weight, offering a simplified dosing regimen that does not require weight-based calculations. This non-weight-based dosing is a first for RSV prevention options in infants.

The CDC’s Advisory Committee on Immunization Practices is expected to meet later this month to discuss recommendations for ENFLONSIA’s use in infants. Merck intends to make the drug available in the U.S. before the start of the 2025-2026 RSV season, with ordering beginning in July.

While ENFLONSIA has been approved for use, it is not recommended for infants with a history of serious hypersensitivity reactions to any component of the drug. The most common adverse reactions observed were injection-site erythema, injection-site swelling, and rash.

This approval follows Merck’s commitment to developing innovative health solutions and adds to its portfolio of medicines and vaccines aimed at preventing and treating diseases. The information provided here is based on a press release statement from Merck & Co., Inc.

In other recent news, Merck & Co. Inc. has reported successful Phase 3 trial results for its cholesterol drug, enlicitide decanoate, which showed significant reductions in LDL cholesterol levels. The trials, known as CORALreef HeFH and CORALreef AddOn, demonstrated enlicitide’s effectiveness compared to placebo and other oral non-statin therapies. If approved, enlicitide could become the first oral PCSK9 inhibitor in the U.S., providing a convenient alternative to injectable treatments. Meanwhile, BMO Capital has maintained its Market Perform rating for Merck, noting potential short-term challenges despite a promising long-term oncology strategy. In contrast, Goldman Sachs reaffirmed its Buy rating, highlighting Merck’s expansive oncology strategy and potential commercial opportunities exceeding $25 billion by the mid-2030s.

Additionally, reports have emerged of Merck engaging in acquisition talks with MoonLake Immunotherapeutics, a Swiss biotech firm, for over $3 billion. Although the initial offer was turned down, discussions may resume, reflecting Merck’s strategy to enhance its drug pipeline through strategic acquisitions. This potential acquisition aligns with Merck’s commitment to expanding its portfolio, particularly in light of upcoming clinical milestones for MoonLake’s therapies. Investors are closely watching these developments, as they could significantly impact both Merck’s and MoonLake’s future trajectories in the pharmaceutical sector.

This article was generated with the support of AI and reviewed by an editor. For more information see our T&C.

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