The Food and Drug Administration has approved Merck’s new treatment to protect infants from respiratory syncytial virus (RSV) during their first season of exposure, paving the way for its rollout ahead of the upcoming fall and winter virus season.
The treatment, to be marketed as Enflonsia, will enter a market currently dominated by Sanofi and AstraZeneca’s Beyfortus, a blockbuster monoclonal antibody shot. With FDA approval in hand, Merck expects to begin taking orders in July and plans to deliver shipments before RSV begins spreading widely.
The FDA’s decision offers physicians a new option to combat a virus that leads to thousands of deaths among older adults and hundreds of deaths among infants each year. RSV-related complications are the leading cause of hospitalization in newborns.
“We are committed to ensuring availability of [Enflonsia] in the U.S. before the start of the upcoming RSV season to help reduce the significant burden of this widespread seasonal infection on families and health care systems,” said Dr. Dean Li, president of Merck Research Laboratories, in a statement.
Like Beyfortus, Enflonsia is a preventative monoclonal antibody that delivers antibodies directly into the bloodstream for immediate protection. However, the two products target different parts of the virus, making direct comparisons challenging.
Merck noted that Enflonsia can be administered to infants regardless of body weight, potentially offering more convenience in dosing. In contrast, the recommended dose of Beyfortus varies depending on an infant’s weight.
Sanofi, responding to last season’s nationwide shortage of Beyfortus due to overwhelming demand, announced on Monday it would ramp up production and start shipping doses early in the third quarter. In 2023, Beyfortus generated sales of €1.7 billion ($1.8 billion).
Other RSV vaccines are also available in the U.S. from Pfizer, GSK, and Moderna, but those are approved only for adults or pregnant women. The FDA has paused testing of RSV vaccines in young children as it investigates safety concerns.
All manufacturers, including Merck, are now awaiting the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices (ACIP) meeting scheduled for June 25–27, which will help shape future recommendations for RSV prevention.
In clinical trials, Enflonsia reduced RSV-related hospitalizations in infants by more than 84% and lowered hospitalizations from lower respiratory tract infections by 90% versus a placebo over a five-month period. It also cut instances of lower respiratory infections requiring medical care by more than 60%.
RSV remains a leading cause of lower respiratory infections such as pneumonia, especially in vulnerable populations like newborns and the elderly.
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