FDA Accepts BLA for Pfizer Maternal RSV Vaccine

This week, the FDA accepted the biologics license application (BLA) for the Pfizer RSVpreF investigational RSV vaccine for expecting mothers. Pfizer’s RSV vaccine candidate would be the first vaccine approved for administration to pregnant individuals to help protect against the complications of RSV in infants from birth through six months.

The FDA has set a PDUFA action date of August 2023.

“If approved, RSVpreF would help protect infants at their first breath from the devastating effects of this infectious disease, which though well-known, has been particularly evident throughout this RSV season,” said Annaliesa Anderson, PhD, senior vice president and chief scientific officer, Vaccine Research & Development, Pfizer.

What the Data Says

The FDA submission was based from the positive top-line results from the phase 3 MATISSE (MATernal Immunization Study for Safety and Efficacy), clinical trial, which evaluated the efficacy, safety, and immunogenicity of RSVpreF against MA-LRTI and severe MA-LRTI in infants born to healthy women vaccinated during pregnancy.

Back in November, Pfizer reported its data, and said in a statement that the pre-planned, interim efficacy analysis conducted by an external and independent Data Monitoring Committee (DMC) met the success criterion for one of two primary endpoints.

The observed efficacy for severe medically attended lower respiratory tract illness (severe MA-LRTI) was 81.8% (CI: 40.6%, 96.3%) through the first 90 days of life. Substantial efficacy of 69.4% (CI: 44.3%, 84.1%) was demonstrated for infants over the six-month follow-up period.

Although the statistical success criterion was not met for the second primary endpoint, clinically meaningful efficacy was observed for MA-LRTI of 57.1% (CI: 14.7%, 79.8%) in infants from birth through the first 90 days of life. Efficacy for MA-LRTI of 51.3% (CI: 29.4%, 66.8%) was observed over the six-month follow up period.

These data will also be presented tomorrow at the CDC’s Advisory Committee on Immunization Practices (ACIP) meeting being held.

According to Pfizer, their RSV vaccine builds on foundational basic science discoveries including those made at the National Institutes of Health (NIH), which detailed the crystal structure of prefusion F, a key form of the viral fusion protein (F) that RSV uses to enter human cells. The NIH research showed that antibodies specific to the prefusion form were highly effective at blocking virus infection, suggesting a prefusion F-based vaccine may confer optimal protection against RSV.

After this discovery, Pfizer tested numerous versions of a stabilized prefusion F protein and identified a candidate that elicited a strong anti-viral immune response in pre-clinical evaluations. The bivalent vaccine candidate is composed of equal amounts of recombinant RSV prefusion F from subgroups A and B.

“We look forward to progressing the review of Pfizer’s RSV maternal vaccine candidate with the FDA and other regulatory authorities, given its significant potential to positively contribute to global health in the prevention of RSV in infants,” Anderson stated.