RSV Vaccines: What to Know For Babies, Pregnant Women and Older Adults

Here’s what to know about the different options, who should get them and when.

The two adult vaccines, which were created by Pfizer and GSK, are very similar, both in terms of how well they protect against symptomatic R.S.V. infection and in their side effects. They also work the same way biologically — targeting a protein the virus uses to fuse to human cells — and were developed based on the same decade-old scientific discovery, which is why they’ve emerged at the same time.

In clinical trials, the Pfizer vaccine, called Abrysvo, was 89 percent effective at preventing lower respiratory symptoms (such as cough, shortness of breath or wheezing) in the first R.S.V. season after vaccination, while the GSK vaccine, called Arexvy, was 83 percent effective. There weren’t enough people in either trial to determine whether the vaccines also helped reduce hospitalizations and deaths, but experts anticipate that they will.

The vaccines were somewhat less effective at preventing disease in the second R.S.V. season after people received a shot. However, experts say that R.S.V. doesn’t mutate in the same way that influenza and SARS-CoV-2 do, so there shouldn’t be a need to update the vaccine or re-dose people every year.

“At least in terms of the more severe symptoms from the infection, it did not seem to diminish over the two-year period appreciably,” said Dr. Edward Walsh, a professor of medicine at the University of Rochester Medical Center, who led the Pfizer clinical trial. “This would suggest that right now, we’re probably looking at a vaccine that is not given any more frequently than every two years.”

Out of the roughly 38,000 people who received either vaccine, 20 experienced atrial fibrillation and six developed neurological complications, including encephalomyelitis and Guillain-Barré syndrome, in the weeks after vaccination. More common side effects were fatigue, fever and muscle pain at the site of the injection.

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