FDA Accepts Merck's Biologics License Application for Clesrovimab, an Antibody to Protect Infants from RSV

Merck, known internationally as MSD, has announced that the U.S. Food and Drug Administration (FDA) has accepted its Biologics License Application for clesrovimab (MK-1654). This investigational monoclonal antibody is designed to protect infants from respiratory syncytial virus (RSV) during their initial RSV season. The FDA has established June 10, 2025, as the target date for their decision under the Prescription Drug User Fee Act (PDUFA).

Dr. Paula Annunziato, senior vice president of infectious diseases and vaccines at Merck Research Laboratories, highlighted the importance of this development. Despite progress in preventing RSV, there remains a significant need for effective solutions to safeguard infants. Clesrovimab, pending approval, aims to be available for the 2025-26 RSV season as the first single-dose immunization for infants, offering protection regardless of their weight throughout their first RSV season.

The application for clesrovimab is backed by results from the Phase 2b/3 CLEVER trial, a randomized placebo-controlled study. This trial involved administering a single dose of clesrovimab to healthy preterm and full-term infants, assessing its efficacy in preventing RSV. Additionally, interim results from the ongoing Phase 3 SMART trial, which compares clesrovimab to palivizumab in infants and children at a higher risk for severe RSV, support the application. These findings were presented at IDWeek in October 2024.

Merck plans for clesrovimab to be ready for healthcare providers to order by July 2025, ensuring its availability for the subsequent RSV season. Clesrovimab is an investigational monoclonal antibody with an extended half-life, developed to provide passive immunization against RSV. Designed for infants, regardless of weight, it is intended to offer swift and lasting protection from mild to severe RSV during their first season.

Merck has emphasized its commitment to ensuring global access to clesrovimab, especially in low- and middle-income countries. The company is actively developing strategies and partnerships to make this intervention accessible worldwide. Their efforts include submitting licensure applications to meet global needs for RSV prevention.

RSV is a highly contagious virus causing widespread seasonal infections, similar to influenza, with significant impact on infants and older adults. There is a pressing need for preventive measures for both healthy and high-risk infants. Globally, RSV is a leading cause of hospitalization in infants under one year and a significant cause of mortality in low- and middle-income regions. It can result in severe respiratory conditions such as bronchiolitis and pneumonia, leading to approximately 3.6 million hospitalizations and 101,000 deaths annually among children under five. In the United States, RSV season typically begins in fall and peaks during winter, though timing can vary by region.

Merck, known as MSD outside North America, has been a leader in scientific innovation for over 130 years, dedicated to improving global health. The company strives to be a premier research-focused biopharmaceutical entity, committed to advancing disease prevention and treatment for both humans and animals. Merck fosters a diverse, inclusive workforce and upholds sustainable, responsible operations to ensure a healthy future for all communities.