In 2023, two new vaccines against respiratory syncytial virus (RSV), which kills thousands of older adults annually in the U.S., hit the market. As millions of people aged 60 and older received the shots, researchers watched and waited to see whether the efficacy numbers seen in clinical trials, which were quite high, would be mirrored in the real world.
“There was a little concern that maybe these vaccines will not turn out to be quite as potent as they appeared,” says Dr. Edward Walsh, a professor of medicine at the University of Rochester. The trials had rolled out in the later phases of the COVID-19 pandemic, when there wasn’t as much RSV circulating as usual, which made some researchers wonder how later studies would play out.
However, in a study published Sept. 18 in JAMA Network Open looking at 14.8 million seniors, researchers at the U.S. Food and Drug Administration found that the vaccines were highly effective, reducing the chances of an RSV-related hospitalization or death by around 80%.
Vaccines protect against RSV in older adults
Since the rollout, a handful of studies have looked at the effectiveness of these two vaccines, which are made by GlaxoSmithKline and Pfizer. “These have all—very interestingly, and comfortingly—really paralleled and mimicked the exact results of the efficacy trials,” says Walsh, who was not involved in the new study. But this new work examines the entire U.S. population over 65 who are enrolled in Medicare, which is “vastly greater than the other studies,” he says. So these results are particularly reassuring. In general, both vaccines performed similarly.
The study found that people who received an RSV vaccine were more likely to live in affluent areas and more likely to have been vaccinated for flu and COVID, raising the question of whether their higher survival numbers have to do with access to health care. However, when researchers performed an analysis meant to test for whether access to health care was a factor, the high efficacy of the RSV shot remained. “That was nice to see, that the data really was identical,” says Walsh.
Do people need RSV vaccine boosters?
One of the big questions now is whether and when to give people another shot, says Walsh. Many of the people in the target population received them in the first year they were available, so much so that an RSV vaccine released in 2024, Moderna’s mRNA version, saw less uptake, he says.
Would giving people another shot two or three years after their first refresh their immunity to the virus? That’s a subject of active research. The second time an RSV shot is given, “you don’t get the same vigorous antibody response that you got when you gave the vaccine for the first time, and whether that is important, I don’t think we really know,” Walsh says. (Flu vaccines, by contrast, require annual shots because strains change so much from year to year that this is the best way to get protected.) Researchers will need to explore this in more detail before patients get a recommendation.
While this new study confirms that these RSV vaccines protect against the worst outcomes of the virus, work to develop vaccines against other viruses, such as parainfluenza, is ongoing. And there could be more broad-spectrum options available someday.
“It may very well be that the ultimate goal would be some sort of a respiratory vaccine that would cover multiple viruses,” Walsh speculates. “One of the thoughts is, well, maybe you can stimulate the innate immune system in a non-specific way such that it would prevent any viral infection.” Working from the observation that having one virus often protects people from getting another, researchers have been delving into new ways of inducing immunity. “These are the kinds of things that immunologists are thinking about,” he says.
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