FDA advisors vote in favor of Pfizer’s RSV vaccine to protect infants

Key takeaways:

• FDA advisors voted 14-0 in support of a maternal RSV vaccine’s effectiveness.
• Four advisors voted against a statement on the vaccine’s safety.

An FDA advisory committee on Thursday voted in favor of a respiratory syncytial virus vaccine that would be administered to pregnant people to protect their infants.

The vote came just over 2 weeks after the FDA approved the first ever vaccine against RSV, GSK’s Arexvy, for adults aged 60 years or older.

RSV is a common respiratory infection that can cause serious illness, especially in infants and older adults. A surge of RSV stretched hospital capacity late last year, and the virus was part of a winter tripledemic of respiratory diseases, alongside COVID-19 and influenza.

The FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) voted 14-0 in agreement that data showed the Pfizer vaccine is effective at preventing RSV in infants during their first 6 months after birth when given to pregnant patients in the second or third trimester.

Responding to a second question on whether data demonstrated an adequate safety profile for the vaccine, four of the 14 VRBPAC members voted “no.”

Phase 3 data presented by Pfizer showed that at 90 days after birth, the vaccine’s efficacy was 57.1% (99.5% CI, 14.7%-79.8%) against RSV-positive medically attended lower respiratory tract illness (MA-LRTI) and 81.8% (99.5% CI, 40.6%-96.3%) against RSV-positive severe MA-LRTI in infants.

One adverse event noted in documents prepared for the meeting was preterm birth — or birth at less than 37 weeks’ gestation — which was reported in 5.7% (95% CI, 4.9%-6.5%) of infants in the trial’s vaccine group and 4.7% (95% CI, 4.1%-5.5%) of infants in a placebo group. The difference, according to the FDA document, was not statistically significant.

This, along with the other noted adverse event of low birth weight, was cited as a concern by members of the committee.

Committee member Capt. Amanda Cohn, MD, director of the CDC’s Division of Birth Defects and Infant Disorders, voted “yes” to both questions.

“To me, enrolling more people in these clinical trials and having really strong post-licensure evaluations because you still want to check on all outcomes will be what we need to reassure the public and to give pregnant women the data that they need to make the decision to get vaccinated,” Cohn said.

Arnold S. Monto, MD, Thomas Francis, Jr. Collegiate Professor of Public Health at the University of Michigan School of Public Health, also voted “yes” to both questions.

“I'm troubled as everybody is by the prematurity issue and I'm not sure that running it through another ‘maybe’ season is going to give us an answer,” Monto said. “But I'm convinced that we have evidence and evidence that should give us some degree of comfort that we can bite the bullet and move ahead with robust observational studies to help us.”

Committee chair Hana El Sahly, MD, professor of molecular virology and microbiology at Baylor College of Medicine, was among the four “no” votes on safety.

“I look forward to seeing data from the post-marketing research, but importantly, encourage continued research into vaccines that don't interfere with other antigens,” El Sahly said. “I feel it's unfair that we take the candidate to the larger public.”

Holly Janes, PhD, professor and associate head of biostatistics, bioinformatics and epidemiology at the Fred Hutchinson Cancer Center in Seattle, also voted “no,” and said that there was “too much uncertainty” regarding the safety.

“I think it's a bit different to rely on surveillance studies to sort of confirm what appears to be a safe product,” Janes said. “Whereas here, I think the signals are such that the post-marketing surveillance data would be asked to refute what is sort of a potential hypothesis.”

Henry H. Bernstein, DO, MHCM, FAAP, Healio Pediatrics Peer Perspective Board Member and professor of pediatrics at Zucker School of Medicine at Hofstra/Northwell, also voted “no.”

“The possibility of an alternative for all newborns at birth in the not-too-distant future makes me want to have more information before voting affirmative for the safety of this particular product,” Bernstein said.

Paul A. Offit, MD, Healio Pediatrics Peer Perspective Board Member and director of the Vaccine Education Center at The Children’s Hospital of Philadelphia, was the other member who voted “no.”

“If you're in any sense risking premature births with this vaccine, I think there'll be a big price to pay and I guess I just don't feel we have enough data to be reassuring, so that's why I voted ‘no,’” Offit said.

Monto, one of the last committee members to speak following the votes, was more optimistic.

“This is a disease we've been trying to prevent for half a century, and this is the first time we've had a chance to do it with a vaccine,” Monto said.

The FDA is expected to issue a decision on whether to approve Pfizer’s RSV vaccine for older adults at some point this month. The VRBPAC recommended the vaccine for this population in March.