Merck Gets RSV Vaccine Approval From FDA Pitting It Against Beyfortus

Merck scores a huge win today as it announced that the FDA had approved its vaccine ENFLONISA [clesrovimab-cfor] for the prevention of respiratory syncytial virus (RSV) in newborns and infants who are either born or entering their first RSV season. This is a strong, long-acting monoclonal antibody that was developed to prevent RSV for such patients. The reason is because it can provide rapid and highly effective protection of this disease through a 5-month period. The main thing for pharmaceutical companies would not only be effectiveness or safety, but how well the drug can sell on the market. Especially in light of several competitors being in place.

With that said, this FDA approval of ENFLONISA from Merck puts it up against big pharma heavyweights Sanofi and AstraZeneca with Beyfortus. What is not guaranteed to, but might give a competitive edge for ENFLONISA is that it can be dosed to any patient regardless of what their weight is. Whereas, with respect to Beyfortus, a patient’s weight is taken into account for specific dosing. It is not going to be easy to go up against these two big pharma companies, because in 2023 they generated $1.8 billion in revenues for it. This is highly impressive, especially when you consider that with high demand, these companies were short on supply to meet it.

They will be ready this time around for the upcoming season for sure, but now they will have to contend with Merck’s rival preventative vaccine. It remains to be seen if the convenience of having one set 105 mg dose of ENFLONISA for any patient, regardless of weight, will translate to stealing market share from Sanofi and AstraZeneca’s RSV vaccine. This FDA approval came just in the nick of time and that is because the company expects to ship this vaccine in July and be ready for the upcoming 2025/2026 RSV season. This U.S. marketing approval is based on results from the phase 2b/3 CLEVER trial (MK-1654-004) which evaluated the use of a single dose of ENFLONISA administered to preterm and full-term infants (this ranged from birth to the age of 1). Plus, positive data was achieved from the phase 3 SMART trial (MK-1654-007), which pitted ENFLONISA against palivizumab in infants at increased risk of obtaining severe RSV disease.

The trial met its primary and secondary endpoints without any issues. In particular, there was a reduction of RSV-associated respiratory infections compared to placebo through 5 months. In addition, there was the ability for the vaccine itself to achieve a reduction of RSV-associated hospitalizations by 84.3% through 5 months (secondary endpoint of trial). This was achieved with a statistically significant p-value of p<0.001. The thing is that the more severe the disease, the greater the efficacy that was shown in the pivotal Phase 2b/3 CLEVER study. Where Merck might hit a snag is in terms of an expected event later this month, whereby the U.S. Centers for Disease Control and Prevention’s (CDC’s) Advisory Committee on Immunization Practices will possibly make recommendations for the use of ENFLONISA in infants. While there are other RSV vaccines approved, from other big pharma companies like GlaxoSmithKline, Moderna, and Pfizer, they have only been approved for use in adults or women who are pregnant.

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