Food and Drug Administration advisers recommended this week that the agency approve two RSV vaccines for older people, one from Pfizer and another from GlaxoSmithKline.
The next step is for the FDA to approve each vaccine, which could take several months, even though the agency usually follows the advisory committee’s recommendations. After FDA approval, the Centers for Disease Control and Prevention must recommend the shots before they become available to the public. If all of that happens, the shots would be the first vaccines for respiratory syncytial virus to get approved in the U.S.
The FDA advisers' recommendations came in separate meetings on consecutive days. On Tuesday, the Independent Vaccines and Related Biological Products Advisory Committee voted 7-4 to recommend Pfizer's vaccine based on its efficacy, with one abstention. The single-dose shot was shown to reduce the risk of illness from respiratory syncytial virus by as much as 86% among people ages 60 and up, according to Pfizer.
Then on Wednesday, the committee's 12 voting members unanimously recommended GSK's vaccine for the same age group based on its efficacy. Trial data published this month in the New England Journal of Medicine showed that the shot lowered the risk of symptomatic illness by 83% and of severe illness by 94% in people ages 60 and up.
RSV causes lower respiratory illness, although for most healthy adults the symptoms are mild. In serious cases, however, RSV can lead to bronchiolitis, which inflames airways and clogs them with mucus, or pneumonia.
Older people and infants are particularly vulnerable to such outcomes. RSV kills more than 10,000 people ages 65 or older and around 300 children under 5 every year in the U.S. Cases spiked dramatically among infants this winter, which overwhelmed children’s hospitals — a reminder of the virus’s threat.
Some advisory committee members seemed to have more hesitations about Pfizer's shot than GSK's. Several of the experts expressed concerns that not enough participants in Pfizer's trial got infected with RSV to adequately assess the shot's efficacy.
In terms of its safety, some advisers worried about the Pfizer vaccine's potential association with Guillain-Barré syndrome, a rare neurological disorder that damages nerve cells and causes muscle weakness or paralysis. One man in Pfizer’s trial developed Guillain-Barré syndrome, or GBS, after he received the vaccine, and a woman developed Miller Fisher syndrome, a rare nerve disease related to Guillain-Barré.
“It was a 1 in 9,000 risk of GBS, which is concerning,” said Dr. Hana El Sahly, the FDA advisory committee chair.
The FDA has asked Pfizer to conduct another study to evaluate the risk of Guillain-Barré syndrome after its vaccine is approved.
In GSK's trial, meanwhile, the FDA identified one case of Guillain-Barre potentially related to the vaccine, as well as a higher number of incidences of atrial fibrillation (irregular heart rhythm) among vaccine recipients relative to the control group.
“There are some challenges, some possible safety signals, but I think the data warrant a vote of ‘yes,’” Dr. James Hildreth, a committee member and the president of Meharry Medical College, said of GSK's shot.
In terms of other side effects, the most commonly reported in GSK’s trial were injection site pain, fatigue and muscle pain. In Pfizer's, the most common were fatigue, headache, pain at the injection site and muscle pain, according to an FDA briefing document.
Participants in GSK's trial reported side effects more frequently than those in Pfizer’s did.
The race to an RSV vaccine
Several companies have been racing to secure FDA approval for RSV vaccines.
Eleven RSV vaccines are being actively studied in U.S. trials, according to data from PATH, a nonprofit global health organization.
Moderna has said an RSV shot it developed for older adults could be submitted to the FDA by July. Bavarian Nordic expects to have late-stage trial data for its RSV vaccine, which targets the same demographic, by the middle of the year.
The FDA is also reviewing data from trials of a monoclonal antibody injection designed to protect babies from RSV, which functions similarly to a vaccine. The shot, from Sanofi and AstraZeneca, has already been approved in Europe.
Meanwhile, Pfizer has tested its RSV vaccine in pregnant people to see whether the protection can pass to babies in utero. The company said its data suggests the vaccine reduced the risk of severe illness in infants by 82% through their first 90 days of life and by 69% through six months.
But the FDA committee’s vote was limited to the Pfizer vaccine’s use for older people. The agency is still reviewing the data for pregnant people, with a decision expected in August.