A group of advisers to the Food and Drug Administration on Wednesday backed a respiratory syncytial virus vaccine developed by GSK for use in older adults, increasing the chances the agency decides in favor of the shot’s approval later this year.
The panel, which on Tuesday reviewed a competing vaccine from Pfizer, voted unanimously in support of GSK’s vaccine’s effectiveness and 10-2 in favor of its safety, reflecting some lingering concerns around potential side effects.
The FDA does not have to follow the advice of its advisory committees, although it usually does so. The agency’s decision is expected by May.
GSK’s approval application is based on several studies the British drugmaker conducted in older adults. In a large Phase 3 trial, the vaccine, called Arexvy, proved 83% effective in preventing cases of lower respiratory infection caused by RSV infection, when compared to a placebo.
Additionally, GSK also studied its RSV shot when co-administered with influenza vaccines and in immunocompromised individuals. On Tuesday, the advisers had noted the low number of immunocompromised participants in Pfizer’s main study, and discussed those concerns again in reviewing GSK’s vaccine Wednesday.
In both cases, advisers wanted to see more data given the vaccines, if approved, could be used widely across millions of older adults.
“I do very much think that the risk-benefit still needs to be understood better before we embark on what could be an annual vaccination program,” said Amanda Cohn, chief medical officer at the National Center for Immunizations and Respiratory Diseases. “But I did feel like the company did a very good job with this first single-dose safety data.”
A rare immune syndrome known as Guillain-Barré was among the advisers’ chief concerns. Two cases were reported following vaccination with Pfizer’s shot, while GSK observed one case in its Phase 3 study, as well as two cases of a neurological disorder called acute disseminated encephalomyelitis when its vaccine was co-administered with the flu vaccine. One of the patients with acute disseminated encephalomyelitis died 22 days later.
GSK is still conducting additional testing of its shot’s safety, something several panelists were interested in seeing. Post-marketing studies could further detail side effect risks, the added.
But Hana El Sahly, the committee’s chair and a professor of molecular virology and microbiology at Baylor College of Medicine noted the difficulties in collecting data after a vaccine is approved.
“It will take a huge effort to answer the question when we already have indication that there may be a safety issue,” said El Sahly, who voted no on the safety question. “We saw that for example in the COVID effort. The [Centers for Disease Control and Prevention] so beautifully helped us mitigate some of the safety concerns but I don’t know that that's going to happen with every vaccine.”
While advisers appeared more supportive of GSK’s case than Pfizer’s, some wanted to see another year of data to increase their confidence in the shot’s efficacy, as well results from a greater number of adults over the age of 80. They had made similar points when reviewing Pfizer’s data on Tuesday.
”I think we [the committee] all have some hesitation,” said Steven Pergam, medical director of infection prevention at Seattle Cancer Care Alliance. “But I’m very excited about the possibility of an RSV vaccine being available and the efficacy data that was presented was robust and included populations I think are interesting.”
Pergam added that he hopes the public can take confidence from the care with which the committee has reviewed the two vaccines.
If approved, GSK’s vaccine could quickly become one of its leading vaccines, with company executives recently predicting it could be as successful as its shingles shot Shingrix. Evan Wang, an analyst at Guggenheim Securities, has forecast that GSK’s peak annual sales could reach $2.8 billion, according to Reuters.
Additional data on the company’s candidate will be available in April.