Pfizer's maternal RSV vaccine filing gets priority review, setting up showdown with AstraZeneca, Sanofi

Pfizer is ready to ram home its advantage in the respiratory syncytial virus (RSV) maternal vaccine race. With onetime close rival GSK still stalled, the Big Pharma has put itself on course to receive a landmark approval by August and go on to challenge AstraZeneca and Sanofi’s long-acting antibody for the market.  

In November, Pfizer stopped a pivotal trial of its bivalent RSV prefusion vaccine candidate RSVpreF early after an interim analysis. The study linked administration of RSVpreF during pregnancy to 81.8% efficacy against severe medically attended lower respiratory tract illness over the first 90 days of the baby’s life. And, while the study missed a co-primary endpoint, Pfizer had seen enough to race to regulators.

Now, the FDA has accepted a filing for approval of RSVpreF for priority review, teeing Pfizer up to receive a decision in August at the latest. Barring a seismic shock setback, RSVpreF will become the first maternal vaccine approved for the prevention of RSV in infants from birth through 6 months.

GSK was racing Pfizer for that crown going into 2022, but its challenge imploded one year ago, when it stopped enrollment and vaccination in three maternal RSV vaccine clinical trials in response to a safety assessment. Talking to Fierce Biotech earlier this month, GSK’s head of vaccine R&D, Phil Dormitzer, M.D., Ph.D., wouldn’t commit to restarting the maternal vaccine trials. 

The removal of GSK from the running, at least for now, leaves AstraZeneca and Sanofi’s long-acting antibody nirsevimab as the chief threat to Pfizer. Nirsevimab and RSVpreF could win approval in the U.S. within weeks of each other, with the FDA accepting the antibody for review at the start of the year and giving AstraZeneca and Sanofi a decision date in the third quarter. 

Pfizer’s maternal vaccine will provide protection from the moment the baby is born, unlike nirsevimab, which is administered after birth, but its phase 3 data failed to blow the antibody away on the efficacy front. With the caveat that cross-trial comparisons can be unreliable, nirsevimab appears to have an efficacy edge over RSVpreF in some regards.