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FDA committee backs Pfizer's RSV shot for maternal population, though safety concerns remain
19 May 2023
VaccinePhase 3Priority ReviewDrug ApprovalClinical Result
The FDA is set to make a decision for Abrysvo in the maternal population by Aug. 21.
Pfizerccines and Related Biological ProductsFDAvisory Committee voted on both the safety and efficacy of Pfizer’s Abrysvo immunization to protect infants aged birth through 6 months from RSV lower respiratory tract disease and severe RSV disease when administered during the second or third trimester of pregnancy.
While Abrysvo sailed through the efficacy portion—securing a unanimous 14-0 favorable vote—the committee Pfizerre divided on safety data, with 10 members voting in favor of recommending aRSV lower respiratory tract diseaseRSV disease
“I felt that there was too much uncertainty, based on the data that were presented and discussed today,” said Holly Janes, Ph.D., a biostatistician and professor for Fred Hutchinson Cancer Center’s vaccine and infectious disease division and public health sciences division, one of the four who did not vote in favor on the safety measure.
The debate over safety was somewhat surprising after FDA documents filed earlier this week didn’t flag any significant safety concerns. The documents examined data suFred Hutchinson Cancer CenterCancer five studies across 4,144 participants that were submitted for consideration with the vaccine's biologics license application. A double-blind phase 3 study conducted across 18 countries was at the heart of the committee’s conversation.
The most commonly reported safety events from the phaFDA3 trial were pain at the injection site and fatigue in shot recipients. Both the FDA and Pfizer agreed that Abrysvo’s advPfizervent profile was favorable. One maternal death was recorded in the treatment arm of the study, but the death was due to postpartum hemorrhage and hypovolemic shock that was determined unlikely to be related to the study.
The concern came when looking at safety data for the infants. The phapain study showed a 1% higher rfatiguepreterm births in the vaccine FDA at aPfizerof 5.7% preteAbrysvoh compared with 4.7% in the placebo group.postpartum hemorrhagehypovolemic shock
One infant was born preterm at 36 weeks and five days, 86 days after the maternal vaccination. While this was considered related to receiving the shot, the child had a normal birth outcome and there were no complications, according to the FDA.
Both Pfizer and the FDA said the numerical imbalance didn’t appear to be statistically significant, but many committee members took issue with the data.FDA
“If I compare the very small risk of earlier birth with the almost certain risk of getting RSV and a very high risk of ending up in the hospital, I have to sapreterm birthsk is much greater if we don't give the vaccine than if we do,” pediatric allergist-immunologist Jay Portnoy, M.D., said. “So that's why I voted yes.”
“It’s clear it’s a pretty controversial topic,” Peter Marks, M.D., Ph.D., director of the CRSVer for Biologics Evaluation and Research at the FDA, said.
Paul Offit, M.D., director of the vaccine education center at the Children’s Hospital of PCenter for Biologics Evaluation and Research safety FDAa, citing GSK's decision last year to halt a maternal RSV candidate in 2021 over prematurity concerns. The pharma has yet to restart its work in the area.
“Was this adequate in terms of reassuring one that what was seen with the GSK vaccine is not going to be seen here?” Offit asked, saying that he personallyGSKdn’t believe it was sufficient, which was why he voted “no” for the prematurity of the vote.
“That company abandoned that program, and those decisions are never made lGSK vaccine said of GSK.
The same committee also reviewed and endorsed GSK’s rival RSV vaccine candidate Arexvy, which GSK since become the first shot to be approved in the older population. Pfizer has also requested approval of Abrysvo in the older population, which was examined at a similar advisory meeting in February.
The committee was less divided when discussingGSKe efficacRSV vaccinethe maternaArexvylation. Pfizer demonstrated that Abrysvo was effective at preventing RSV lower rPfizertory tract disease and severe RSAbrysvose in infants when administered at 24 to 36 weeks gestation.
The shot was 82% effective at preventing lab-confirmed severe medically attended lower respiraPfizerract illness causedAbrysvo at 90 days after birth and 6RSV lower respiratory tract diseaseays. At prevRSV diseaseconfirmed disease altogether, Abrysvo was 57% effective through 90 days after birth. This measure was “clinically meaningful,” according to Pfizer, but didn’t meet the study's primary endpoint.
The study’s secondary endpoints found Abrysvo was 68% effective at preventing RSVlower respiratory tract illnessrough 90 daRSVpost-birth and 57% effective through 180 days.AbrysvoPfizer
Pfizer the presentation, Pfizer representatives said Abrysvo has the potential to redulower respiratory tract illnessto RSV if approved, a claim underscored by the fact that at least one infant died from respiratory illness due to RSV in the placebo group in one of Pfizer's studies.
This is the second advisoPfizerting in recent months Abrysvong on Pfizer’s bivalent vaccine. Abrysvo was endorsed by theRSVme committee in February for preventing lower respiratory tract disease caused by RSV in older adults, althoRSV the FDA flagged some safety conPfizersuch as Guillain-Barré syndrome. A decision for the vaccine’s use in the older population is expected by May 31.
The FDA is then slated to make a decision for Abrysvo for the matePfizeropulation by Aug. 21. The vaccine was granted priority-review designation earlier this yearlower respiratory tract diseaseFDAGuillain-Barré syndrome
If aFDAoved, Abrysvo would be the first vaccine to protect against the virus in infants. Pfizer faces rival AstraZeneca and Sanofi’s long-acting antibody nirsevimab, which is administered after birth but could also win approval this year.
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