Pfizer Seeks Expanded Approval for Abrysvo Following Positive Phase III RSV Vaccine Results

Pfizer has recently announced preliminary results from its MONeT Phase III clinical trial, which indicate that its vaccine Abrysvo is effective in providing immunity against respiratory syncytial virus (RSV) in adults aged 18 to 59. The vaccine successfully met the trial's key immunogenicity goals, showing a comparable neutralizing response to both RSV-A and RSV-B strains when compared to its performance in older adults, as established in the RENOIR study. This earlier study confirmed the vaccine's safety and efficacy.
The latest data reveal that Abrysvo vaccination led to a significant fourfold rise in serum neutralizing titers against both RSV strains one month post-vaccination. Moreover, the vaccine was found to be well-tolerated, with a safety profile aligning with previous findings. Annaliesa Anderson, Pfizer's vaccine research and development lead, has described the results as "encouraging," suggesting that they offer robust evidence of Abrysvo's protective capabilities in younger adults susceptible to RSV-related diseases.
Pfizer plans to submit these findings to health regulatory authorities with the aim of expanding Abrysvo's approval for a wider demographic. If successful, Abrysvo could become the first RSV vaccine available for adults aged 18 and above. The vaccine received FDA approval in June 2023, shortly after its main competitor, Arexvy, developed by GSK. Both vaccines are currently approved for preventing lower respiratory tract disease in adults over 60.
In August 2023, Abrysvo's label was expanded to include its use in pregnant women during the last stages of their third trimester to protect their newborns from RSV. Despite this broader application and a potentially larger patient base, Abrysvo's market performance has not matched that of Arexvy. Pfizer's CFO, David Denton, expressed disappointment with Abrysvo's results during a November 2023 investor meeting. Meanwhile, GSK's Arexvy was making significant strides towards becoming a blockbuster drug, with GSK reporting in its third-quarter earnings that Arexvy had dominated retail vaccinations in the U.S. and generated nearly $860 million in revenue during its first full quarter.
GSK is also pursuing an expanded label for Arexvy, focusing on the adult population. In October 2023, the company shared initial data from a Phase III trial involving individuals aged 50 to 59, suggesting that the vaccine was equally safe and effective in this younger demographic as it is in the population for which it is currently approved.