Advisers to the Food and Drug Administration on Tuesday recommended approval of what could be one of the first vaccines for respiratory syncytial virus, but expressed concerns about some of the study results its developer, Pfizer, has gathered so far.
At a meeting convened by the FDA, panelists voted 7 to 4, in separate votes, that Pfizer’s data support the safety and effectiveness of the vaccine in adults 60 years or older. One committee member abstained in each vote.
While the FDA doesn’t have to follow the advice of its committees, it usually does. The regulator is expected to decide whether to approve the vaccine, called Abrysvo, by May.
Pfizer’s application is mainly based on the results of a Phase 3 trial that read out last August. Pfizer reported the shot was 67% effective at preventing moderate disease, or infections with at least two symptoms, in adults. That same trial found the shot was 86% protective against more severe disease, defined as RSV-associated lower respiratory tract illness with at least three symptoms. Pfizer also said the shot was generally well-tolerated.
The results followed a similar Phase 3 readout from rival GSK, positioning both companies to bring to market a shot for RSV, a common, cold-like virus that can be deadly in the elderly and young children. Between 6,000 to 10,000 deaths occur from RSV in older adults every year.
Despite acknowledging the need for such a shot, FDA advisers expressed some skepticism. Specifically, panelists cited the low representation of high-risk participants in Pfizer’s trial, short study follow-up, and rare instances of an autoimmune condition called Guillain-Barré. They also wanted to see more data showing it is safe to co-administer the shot with flu vaccines.
“We’ve not had an RSV vaccine at all,” said Adam Berger, the director the National Institutes of Health’s division of clinical and healthcare research policy, and a panelist who voted in favor of the vaccine. “This would be potentially able to protect older individuals, but ... we’re missing a lot of data to show that it really is effective.”
Advisers noted particular concerns about the potential risk of Guillain-Barré, a rare syndrome that affects the peripheral nerves. Two trial participants were diagnosed with the condition, but the cases weren’t considered related to the vaccine. The agency suggested Guillain-Barré be listed as a potential risk factor on the shot’s label, and recommended a post-marketing safety study to monitor any links to vaccination.
Panelists also said Pfizer’s study didn’t include enough participants over 80 or with weak immune systems, two groups with the greatest need for a vaccine. They also wanted to see more evidence of the shot’s durability.
“I would really like to have seen them [Pfizer] complete the study to get at least another year’s worth of RSV data, and then I would feel more comfortable about the results,” said Stanley Perlman, a pediatric infectious disease expert at the University of Iowa, who abstained from voting on the shot’s safety but supported its efficacy.
Ultimately, the advisers backed Abrysvo, although not all the panelists voted the same way on the FDA’s separate questions regarding the shot’s safety and effectiveness. “I can’t help but think about the risk-benefit analysis and ratio of the amount of severe disease potentially that could be prevented with this vaccine,” said committee member Daniel Feikin, a respiratory disease consultant.
A study is currently underway to test whether Abrysvo is safe to receive alongside other shots for other infections such as flu or COVID-19. Without that information, Pfizer’s shot “may need to be given separately from flu shots, which would be logistically challenging” and “negatively impact uptake,” wrote SVB Securities analyst David Risinger.
“We believe Pfizer’s vaccine is still more likely than not to be approved despite the lukewarm endorsement from the committee,” Risinger wrote, but “it is possible” the FDA could request more data, delaying its arrival.