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.