The U.S. Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) voted to recommend Merck & Co Inc’s MRK Enflonsia (clesrovimab-cfor) as an option for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in infants younger than 8 months of age who are born during or entering their first RSV season.
With a five-to-two majority, RFK Jr.’s newly constituted committee made its first ruling. This body was formed after RFK Jr. entirely replaced the previous 17-member panel with his own selections.
The ACIP also voted to include Enflonsia in the Vaccines for Children Program, an essential step in ensuring broad access to this preventive option for infants.
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Enflonsia is a preventive, long-acting monoclonal antibody (mAb) designed to provide direct, rapid, and durable protection through 5 months, a typical RSV season, with the same dose regardless of weight.
A typical RSV season usually spans autumn to spring of the next year. The U.S. Food and Drug Administration (FDA) approved Enflonsia in June.
The approval is based on results from the pivotal Phase 2b/3 CLEVER trial (MK-1654-004) evaluating a single dose of Enflonsia administered to preterm and full-term infants (birth to 1 year of age). The trial met its primary and key secondary endpoints.
Enflonsia demonstrated a reduction in incidence of RSV-associated medically attended lower respiratory infections (MALRI) requiring ≥1 indicator of lower respiratory infection (LRI) or severity compared to placebo through 5 months (primary endpoint) by 60.5% (incidence rates: Enflonsia, 0.026; placebo, 0.065).
Enflonsia demonstrated a reduction in RSV-associated hospitalizations through 5 months (key secondary endpoint) by 84.3% (incidence rates: Enflonsia, 0.004; placebo, 0.024), showing increasing efficacy with increasing disease severity.
Merck plans to make Enflonsia available for physicians and healthcare administrators to order in July 2025. Shipments will be delivered before the start of the 2025-2026 RSV season.
The ACIP’s recommendation for Enflonsia is provisional and will become official once it is reviewed and finalized by the CDC Director or the Health and Human Services Secretary (in the absence of a CDC Director).
Price Action: MRK stock is up 0.33% at $79.10 during the premarket session at last check Friday.
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