Merck RSV drug baby wins FDA nod, but CDC committee will recommend using it
A Merck drug developed to prevent infant respiratory comprehensive virus (RSV) has won FDA approval to introduce competition to products already obtained by Pfizer and Sanofi.
The antibody’s Monday regulatory decision (known in development as Creslovimab) covers its use during newborns and infants entering its first RSV season, which spans the fall and winter. For those born in the RSV season, Creslovimabu will be managed shortly after birth. Merck will sell its new products under the brand Enflonsia.
RSV infection usually causes symptoms similar to the common cold in healthy people. But in infants and older people, diseases caused by RSV infection can lead to life-threatening respiratory complications. In the past three decades, the only product that can protect babies from lower respiratory tract diseases caused by RSV is hyposamine, an antibody developed and commercialized by Astrazeneca. This product is approved for use only in premature babies. The antibody has a short half-life and requires monthly administration. Recent advances in RSV research have led to products, such as Merck's Enflonsia, which require only one injection.
Enflonsia is an antibody designed to last in the body for about five months, enough to protect the baby during typical RSV season. The FDA decision for the product is based on the results of a placebo-controlled Phase 2b/3 clinical trial that recruited 2,858 infants entering its first RSV season. The results showed that the incidence of RSV-related infections was 60.5% lower than placebo compared to placebo compared to placebo. The antibody also resulted in a reduction in hospitalization associated with RSV within five months. The most common adverse effect is injection site reaction. In a 3-stage test comparing Enflonsia to the next ala, Merck's drug is comparable to that of AstraZeneca's products.
Pfizer's presence in RSV is through Abrysvo, a vaccine composed of an engineered version of the RSV F protein antigen. It was first approved for use in the elderly in 2023. Later that year, the vaccine was approved for maternal immunization, where immunization of pregnant mothers results in the production of antibodies delivered to the baby. Last year, the FDA extended the Abrysvo label to include adults aged 18 to 59. Pfizer reported $755 million in Abrysvo revenue for all approved uses in 2024, down 15.1% from the previous year. The company attributed the decline to a substantial reduction in U.S. vaccination rates for older Americans, partly offset by strong demand for maternal immunity.
Sanofi's Beyfortus was approved in 2023 and has become a major product for RSV baby protection. Similar to Merck's new RSV product, Beyfortus is a long-acting antibody that, although technically a drug, is designed to protect like a vaccine. The antibody is designed with technology that gives it a half-life of about five months. Sanofi R&D director Jon Heinrichs told Medcity News in 2023 that the advantage of Beyfortus' maternal immunity is that administrative seasons can be used regularly to provide maximum protection during the RSV season. By contrast, the timing of birth can only be estimated, so it may weaken when the RSV season arrives or during this season, and antibodies produced by maternal immunity may no longer be effective.
Beyfortus is injected as a single intramuscularly. Sanofi reported revenue of $1.6 billion in 2024, more than double sales in the previous year. Unlike the dose of Beyfortus, Merck's ENFLONSIA is given at the same 105 mg dose regardless of the patient's weight. Merck Research Lab president Dean Li said in a prepared statement that the company is committed to getting Enflonsia to provide before the upcoming RSV season begins.
Recommendations for vaccine use come from the Advisory Committee on Immunization Practice (ACIP) of the Centers for Disease Control and Prevention. The committee is scheduled to be held from June 25 to 27. Merck said it expects ACIP to discuss Enflonsia at the meeting.
When the ACIP conference is held, it will have a brand new lineup. The Ministry of Health and Human Services announced on Monday that 17 current members of the committee have been removed from office. HHS said 13 of the members were appointed President Biden in 2024. All members will be replaced by new members currently being considered. HHS Secretary Robert F. Kennedy Jr. Kennedy continues to assert that there is no evidence that the Independent Advisory Committee has been “as a rubber stamp on the industry’s profit agenda.”
The American Medical Association has questioned the firing of ACIP members and noted that the committee is trusted to provide scientific and data-driven advice and guidance.
“Physicians, parents, community leaders and public health officials all rely on them for clinical guidance, public health information and knowledge,” said Dr. Bruce Scott, president of the association, in an emailed statement. “Today, the action of deleting 17 current members of ACIP undermines trust and subverts transparency, which saves countless lives. This move will further intensify the spread of vaccines to prevent the disease as the measles outbreak and the decline in the vaccination rate of routine children.”
Photo: Christopher Occhicone/Bloomberg
