Advisers to the Food and Drug Administration recommended that the agency should approve the first vaccine to protect infants from RSV, or respiratory syncytial virus. But some of the experts expressed reservations about the adequacy of data in support of the vaccine's safety.

In a two-part vote, the experts voted unanimously, 14-0, that the available data support the effectiveness of the Pfizer vaccine in preventing severe RSV-related respiratory illness. They then voted 10-4 that the data supports the vaccine's safety.

RSV is a leading cause of infant hospitalization in the U.S. From 58,000 to 80,000 children younger than 5 years old are hospitalized each year with RSV infections, according to the Centers for Disease Control and Prevention. Infants 6 months old and younger are at elevated risk for severe RSV illness.

The votes came after a day of testimony and discussion during a public meeting of the agency's expert panel on vaccines. The FDA isn't bound to follow the advice of its expert panels, but it usually does. A decision on the vaccine for infants is expected by late August.

The vaccine isn't given to babies. Instead, pregnant people are immunized during the late second to third trimester of pregnancy. The antibodies they develop against RSV pass to the fetus in the womb and later protect the newborn.

A clinical study involving 7,400 people found the vaccine had 81.8% efficacy in preventing severe respiratory illness caused by RSV within three months after birth and 69.4% in the first six months.

There was some evidence that those who got vaccinated might have been more likely to give birth prematurely. And committee members worried about pregnant people getting the vaccine at the same time as some other vaccines, such as TDAP (tetanus-diphtheria-pertussis), because it could interfere with their effectiveness.

"I worry that if preterm births are in any way a consequence of this vaccine, that would be tragic," said Dr. Paul Offit, professor of pediatrics at The Children's Hospital of Philadelphia. He voted no on the adequacy of safety data.

The same Pfizer vaccine is under FDA review to protect people 60 and older people from RSV. Advisers voted to support approval of the vaccine at February meeting.

Separately, in a first, the agency approved an RSV vaccine from drugmaker GSK in early May for people 60 and older.

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All right. The first vaccine to protect babies against one of the most common respiratory viruses took a major step forward today. Advisers to the Food and Drug Administration endorsed the vaccine to guard newborns against RSV. NPR health correspondent Rob Stein joins us now. Hey, Rob.


CHANG: So I remember RSV surged over the winter, and it was such a big deal at the time. But can you just remind us how big of a problem RSV is in a typical year?

STEIN: Sure. You know, yeah, RSV came roaring back with a vengeance last fall, playing a big role in last winter's miserable tripledemic (ph), you know, overwhelming children's hospitals around the country. But even in normal years, RSV is a huge problem each fall and winter. Most kids will catch RSV in their first year of life. For most, RSV just causes a cold. But 2 or 3% of newborns will be hospitalized for RSV, making it the leading cause of hospitalization for very young babies. As many as 80,000 babies end up in the hospital each year because of RSV. And between 100 and 300 die, according to the CDC. Here's Dr. Eric Simoes from the Children's Hospital of Colorado, who spoke on behalf of Pfizer, which developed the new vaccine.

ERIC SIMOES: There's nothing more distressing for parents than the frightened look of that 3-month-old infant struggling to breathe, being unable to feed.

STEIN: The first vaccine to protect older people, who are also at high risk for RSV, was just approved by the FDA. But despite decades of efforts to find a vaccine that can protect babies, this is the first time an RSV vaccine for newborns has made it this far.

CHANG: Oh, really? So is there something special about this vaccine to have made it so far?

STEIN: Yeah, it's interesting. You know, we typically think of vaccines as a shot we get to protect ourselves against, say, the flu or COVID. But there's a twist with this one. It's a shot that pregnant people get six to nine months into their pregnancies to protect their babies for the first six months after they're born. It works by stimulating the pregnant person to generate protective antibodies, which are then passed to the developing fetus in the womb. And in a big study involving thousands of pregnant people conducted by Pfizer, the shot was almost 82% effective at protecting babies against severe RSV in their first three months of life and 69% effective at protecting them against severe disease in the first six months.

CHANG: That sounds pretty good. Are there any concerns about the vaccine, any downsides?

STEIN: Yeah. You know, a previous experimental vaccine ended up actually making RSV worse without protecting babies. And even though that was way back in the '60s, that specter has kind of cast a shadow over this whole field. Now, there's no signs of that problem with this vaccine, but there was a lot of concern about a little hint that those who got vaccinated might be more likely to give birth prematurely. Here's Dr. Paul Offit from the University of Pennsylvania.

PAUL OFFIT: I worry that if the preterm births are in any way a consequence of this vaccine, that would be tragic.

STEIN: But then Dr. William Gruber from Pfizer argued that the clear benefits of the vaccine outweigh unproven risks.

WILLIAM GRUBER: The question is, do you hold hostage the potential benefits of the vaccine for something for which you have no statistical significance?

STEIN: And in the end, the FDA advisory committee voted unanimously that the vaccine is effective. But the committee then voted 10 to 4 that the vaccine is also safe.

CHANG: OK. So the committee likes what they see in this vaccine. What happens next?

STEIN: The FDA will now consider the advisers' votes and decide what to do, and it has to make a decision by August 21. I should mention that the agency is also considering approving this vaccine for older people, too, as well as what's known as a monoclonal antibody to protect babies. So, you know, after decades of frustration, trying to find ways to fight RSV, there's finally some possible options coming to protect, you know, this fall and winter.

CHANG: That's great news. That is NPR health correspondent Rob Stein. Thank you so much, Rob.

STEIN: Oh, you bet.

(SOUNDBITE OF MASEGO SONG, "YOU NEVER VISIT ME") Transcript provided by NPR, Copyright NPR.

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