Merck Announces FDA Acceptance of Biologics License Application for Clesrovimab, an Investigational Long-Acting Monoclonal Antibody Designed to Protect Infants from RSV Disease During their First RSV Season

If approved, clesrovimab has the potential to be available to help address the burden of RSV disease in the U.S. in time for the 2025-26 season

Merck (NYSE:MRK), known as MSD outside of the United States and Canada, today announced the U.S. Food and Drug Administration (FDA) has accepted the Biologics License Application (BLA) for clesrovimab (MK-1654), the company's investigational prophylactic long-acting monoclonal antibody designed to protect infants from respiratory syncytial virus (RSV) disease during their first RSV season. The FDA has set a Prescription Drug User Fee Act (PDUFA), or target action, date of June 10, 2025.

"Despite recent advances in RSV prevention, unmet needs remain for additional effective interventions to help protect infants and continue to help address the burden RSV places on families and the healthcare system. This regulatory milestone, along with promising results from our pivotal studies demonstrating efficacy in the prevention of RSV disease, marks important progress toward our goal of having clesrovimab available in time for the 2025-26 RSV season," said Dr. Paula Annunziato, senior vice president, infectious diseases and vaccines, Global Clinical Development, Merck Research Laboratories. "We look forward to working alongside the FDA on the review of clesrovimab, which, if approved, would be the first and only single dose immunization for infants regardless of weight designed to protect them for the duration of their first RSV season."

The application is supported by results from the pivotal Phase 2b/3 CLEVER trial (MK-1654-004), a randomized placebo-controlled trial evaluating a single dose of clesrovimab administered to healthy preterm and full-term infants (birth to 1 year of age), and interim results from the ongoing Phase 3 SMART trial (MK-1654-007) evaluating the safety and efficacy of clesrovimab versus palivizumab in infants and children at increased risk for severe RSV disease. Data from these trials were presented during IDWeek in October 2024.

If approved, Merck anticipates that clesrovimab would be available for ordering by physicians and healthcare administrators by July 2025, with shipments to arrive in time for the 2025 RSV season.

About clesrovimab (MK-1654)

Clesrovimab (MK-1654) is an investigational, extended half-life monoclonal antibody (mAb) developed as a passive immunization for the prevention of RSV disease. Clesrovimab is designed to be administered as the same single dose, regardless of weight, and is being studied in healthy preterm, full-term and at-risk infants to provide direct, rapid, and durable protection through their first RSV season against mild, moderate and severe RSV.

About Merck's commitment to global supply and access of clesrovimab

Since the discovery of clesrovimab, our investigational respiratory syncytial virus (RSV) monoclonal antibody (mAb), our goal has been to facilitate global access to this intervention. We are diligently developing our regulatory and access strategies, as well as our supply chain to be fit-for-purpose for low- and middle-income countries by utilizing diversified internal investments and external partnerships. The company is working with urgency to submit licensure applications to address unmet needs for RSV prevention globally.

About RSV

Respiratory syncytial virus (RSV) is a contagious virus that causes widespread seasonal infections like the flu, with a worldwide burden in infants and older adults. There is high unmet need for preventative options in both healthy and high-risk infants. Globally, RSV is the leading cause of hospitalization for healthy infants under a year old, and a major cause of death in low- and middle-income countries. RSV can lead to serious respiratory conditions like bronchiolitis and pneumonia, causing an estimated 3.6 million hospitalizations and 101,000 deaths a year worldwide in children under five. According to the CDC, RSV season starts in the fall and peaks in the winter in most regions of the United States, but timing and severity in a given community or region can vary year to year.

About Merck

At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities. For more information, visit www.merck.com and connect with us on X (formerly Twitter), Facebook, Instagram, YouTube and LinkedIn.

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