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FDA panel recommends the first shot to prevent RSV in infants by vaccinating pregnant mothers

Next, the FDA will decide whether to approve Pfizer’s vaccine. The agency said the safety data was “generally favorable” but noted a slightly elevated rate of preterm birth.
A doctor examines a baby with respiratory symptoms
A doctor examines a baby with respiratory symptoms in Cloquet, Minn., in May 2022.Alex Kormann / Star Tribune via Getty Images file

An independent advisory committee to the Food and Drug Administration voted Thursday to recommend a shot that protects infants from RSV by vaccinating their mothers while pregnant.

The 14-person panel unanimously recommended the shot, made by Pfizer, based on its efficacy and voted 10-4 to recommend it based on its safety. 

If the shot is eventually approved by the FDA, it would be the first vaccine that confers protection against respiratory syncytial virus to babies.

“Before the pandemic, RSV was the No. 1 cause of infant hospitalization in the United States, so this is a big deal,” said Dr. Ofer Levy, the director of the Precision Vaccines Program at Boston Children’s Hospital. Levy is a temporary voting member of the FDA panel but wasn’t involved in Thursday’s vote.

In healthy adults, lower respiratory illness caused by RSV is typically mild, but it can be more severe in babies and older adults. The virus kills up to 300 children under 5 every year in the U.S. and up to 10,000 people ages 65 or older, according to the Centers for Disease Control and Prevention. Severe infections can result in pneumonia or bronchiolitis, which inflames airways and clogs them with mucus.

It could take months for the FDA to decide whether to approve the shot, but the agency is likely to follow the advisory committee’s recommendation.

The FDA approved the world’s first RSV vaccine this month, made by pharmaceutical giant GSK, but the shot is only for adults ages 60 and up.

Pfizer also has an RSV shot for older adults up for FDA approval this month. The FDA advisory panel in late February recommended the shot for people ages 60 and up. It’s the same vaccine that would be given to pregnant people.

To protect infants, the shot would be given to pregnant people at 24 to 36 weeks’ gestation; the protective antibodies transfer through the placenta.

The committee members generally praised the vaccine’s efficacy but shared reservations about the duration of protection and a potential risk of preterm birth.

In a clinical trial with nearly 7,400 participants, the vaccine lowered the risk of severe disease from RSV among infants by 82% within roughly three months after birth. By around six months, efficacy was around 69%. Infants 6 months and younger are especially vulnerable to severe cases of RSV.

The shot also lowered the risk of developing respiratory disease from RSV that required doctors’ visits by 51% within about six months. After that, however, the vaccine didn’t appear to make a big difference.

In a briefing document, the FDA said safety data from the trial seemed “generally favorable.” The most common side effects of the shot reported among pregnant women were fatigue, headache, muscle pain and injection site pain.

However, the agency noted that there was a slightly higher rate of preterm births — defined as before 37 weeks’ gestation — among people who received the vaccine (5.7%) versus those who got a placebo (4.7%). The difference wasn’t statistically significant, however, so it’s unclear whether it was vaccine-related.

Both rates were lower than the rate of preterm births in the general population: around 10%, according to the CDC.

Last year, the pharmaceutical giant GSK halted its trial of an RSV vaccine for infants after it showed a higher preterm birth rate among some vaccine recipients.

Dr. Paul Offit, a member of the FDA advisory committee and director of the Vaccine Education Center at Children’s Hospital of Philadelphia, said the outcome of GSK’s trial was relevant to Pfizer’s study, since the two vaccines are similar. 

“I worry that if preterm births are in any way a consequence of this vaccine, that would be tragic in many ways,” Offit said at Thursday’s meeting. He voted against the shot based on its safety.

Pfizer said that if its shot is approved, it would continue to monitor the risk of preterm birth among vaccine recipients. 

Levy said researchers generally pay close attention to any potential risk of preterm birth among vaccines given to pregnant people.

“There’s always the background concern: Are you inducing some inflammation that could be a problem? Because the body reads inflammation as ‘the woman’s no longer safe, let’s get the baby out.’ So you want a fairly bland vaccine,” he said.

But Adam Berger, a researcher at the National Institutes of Health who voted in favor of the shot based on both safety and efficacy, said the vaccine is strongly needed.

“There isn’t another option here for prevention and it really could save a lot of lives,” Berger said.

Eleven RSV vaccines (including GSK’s approved shot) are being actively studied in U.S. trials, according to data provided to NBC News by PATH, a nonprofit global health organization. Six are for older adults, and five are designed to protect infants or children.

A monoclonal antibody injection, which is given directly to infants and functions similarly to a vaccine, has already been approved in Canada, Europe and the United Kingdom. The FDA began reviewing data on that shot in January and is expected to decide this summer or fall whether to approve it.