Merck known as MSD outside the United States and Canada, announced today that the U.S. Food and Drug Administration (FDA) has accepted its Biologics License Application (BLA) for clesrovimab (MK-1654), an investigational long-acting monoclonal antibody designed to protect infants from respiratory syncytial virus (RSV) during their first RSV season. The FDA has set a Prescription Drug User Fee Act (PDUFA) date of June 10, 2025, for a decision on the approval of the application.
RSV is a leading cause of lower respiratory tract infections in infants and young children, resulting in significant healthcare burdens. Although there have been advancements in RSV prevention, there remains a critical need for additional effective interventions to protect infants, particularly during their first RSV season. The FDA’s acceptance of Merck’s BLA for clesrovimab represents a significant regulatory milestone in addressing this gap, with the potential to provide a new option for RSV prevention.
Dr. Paula Annunziato, Senior Vice President of Infectious Diseases and Vaccines, Global Clinical Development at Merck Research Laboratories, emphasized the importance of the FDA’s acceptance of the BLA. “Despite recent advances in RSV prevention, unmet needs remain for additional effective interventions to help protect infants and continue to 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,” Dr. Annunziato said.
If approved, clesrovimab would be the first and only single-dose immunization designed to protect infants from RSV for the duration of their first RSV season, regardless of their weight. This is a significant advantage over existing treatments, which require multiple doses or are dependent on weight-based dosing. Clesrovimab’s long-acting nature means it could offer a convenient and effective way to reduce RSV risk for vulnerable infants.
The BLA submission is supported by data from the pivotal Phase 2b/3 CLEVER trial (MK-1654-004), a randomized, placebo-controlled study that evaluated the efficacy of a single dose of clesrovimab in healthy preterm and full-term infants aged 0 to 12 months. Additionally, interim results from the ongoing Phase 3 SMART trial (MK-1654-007) provide further evidence of the safety and efficacy of clesrovimab in infants and children at increased risk for severe RSV disease. These trials have demonstrated positive outcomes, and data from them were presented during the 2024 IDWeek conference in October.
In the CLEVER trial, clesrovimab showed promising results in preventing RSV infections and reducing the associated healthcare burden. The SMART trial, which compares clesrovimab with the current standard of care, palivizumab, has also provided strong evidence that clesrovimab may offer superior protection for high-risk infants. The ongoing studies will continue to provide important insights into the safety profile and long-term efficacy of the monoclonal antibody.
Merck anticipates that, if approved, clesrovimab will be available for ordering by healthcare providers by July 2025, with shipments arriving in time for the 2025 RSV season. This timeline would allow physicians and healthcare administrators to make the antibody available to infants before the peak RSV season, helping to reduce the burden of RSV disease during its high-risk period.
RSV is a highly contagious virus that leads to severe respiratory illness in infants, young children, and older adults. In the U.S., RSV is responsible for approximately 58,000 hospitalizations and 100 to 500 pediatric deaths each year. While most infants recover from RSV with supportive care, some may require hospitalization due to the severity of the infection. Currently, there are limited preventive options for healthy infants, and the need for a safe and effective long-acting prophylactic therapy is urgent.
Merck’s focus on developing clesrovimab is a direct response to this public health challenge. The company aims to offer a new treatment option for parents and healthcare providers seeking better ways to protect infants from this potentially life-threatening virus. With the FDA’s acceptance of the BLA, Merck is one step closer to achieving this goal.
As RSV continues to pose a significant threat to infant health, clesrovimab represents a potential breakthrough in the prevention of the disease. If approved, it will offer a much-needed solution to reduce RSV-related hospitalizations and deaths, providing a vital tool in the fight against respiratory infections in infants.
For now, Merck will continue to work closely with the FDA as the review process progresses, with the hope that clesrovimab will become a key part of the preventive measures against RSV in time for the 2025-26 RSV season.
