The Food and Drug Administration on Monday approved Merck’s shot designed to protect infants from respiratory syncytial virus during their first season of the virus, bringing to market a rival to a similar treatment from Sanofi and AstraZeneca.
The decision will allow the company to launch the drug, which will be marketed as Enflonsia, ahead of the RSV season that typically kicks off around fall and winter and lasts through the spring. Merck said in a release that it expects orders for the shot to begin in July, with shipments delivered before the virus starts to spread widely.
The approval gives doctors a new treatment option for the virus, which causes thousands of deaths among older Americans and hundreds of deaths among infants each year. Complications from RSV are the leading cause of hospitalization among 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,” Dr. Dean Li, president of Merck Research Laboratories, said in a release.
Merck’s shot will compete against a similar blockbuster treatment from Sanofi and AstraZeneca called Beyfortus, which was in short supply nationwide during the 2023 RSV season due to unprecedented demand.
Both are preventative monoclonal antibodies, which deliver antibodies directly into the bloodstream to provide immediate protection. But each targets a different part of the virus, making it difficult to compare them directly.
Merck’s treatment can be administered to infants regardless of their weight, which the company said may offer convenience in terms of dosing. Meanwhile, the recommended dosage of Beyfortus is based on an infant’s body weight.
Sanofi on Monday revealed an aggressive effort to increase supply of Beyfortus, including a plan to begin shipping the shot early in the third quarter. Last year, Beyfortus booked sales of €1.7 billion ($1.8 billion).
Vaccines for RSV are also available in the U.S. from companies such as Pfizer, GSK and Moderna. But those shots are only for use in adults or in pregnant women. Recently, the FDA paused testing of RSV shots in young children while it evaluates safety concerns.
All of the companies in the market are waiting for a meeting of outside vaccine advisors to the Centers for Disease Control and Prevention from June 25 to 27, when they will form recommendations for RSV shots and other immunizations.
In the mid- to late-stage trial on Enflonsia, the treatment reduced RSV-related hospitalizations by more than 84% and decreased hospitalizations due to lower respiratory infections by 90% compared with a placebo among infants through five months. The shot also reduced lower respiratory infections that required medical attention by more than 60% compared with a placebo through five months.
RSV is a common cause of lower respiratory tract infections such as pneumonia.
