A maternal RSV vaccine to protect infants is one step closer to FDA approval

A federal advisory committee raised questions Thursday about the safety of a proposed vaccine to protect newborns against respiratory syncytial virus or RSV, but ended up voting in favor of its approval.

“This is a disease we’ve been trying to prevent for half a century and this is the first time we’ve had a chance to do it with a vaccine,” said Dr. Arnold Monto, an epidemiologist at the University of Michigan School of Public Health, who voted to support the approval.

The commissioner of the Food and Drug Administration still has to sign off on the RSVpreF vaccine and the Centers for Disease Control and Prevention has to provide guidance on its use before it can become available. Made by pharmaceutical giant Pfizer, the vaccine would be used in pregnancy to help prevent severe disease in infants during their first six months of life.

If given final approval, RSVpreF would become the second RSV vaccine but the first-ever vaccine to protect infants against the worst outcomes of the virus. Final FDA approval is expected in August – in time for this year’s RSV season, which typically starts in late fall.

Respiratory syncytial virus infects nearly every child by age 2 and typically causes cold symptoms. But it’s also the leading cause of hospitalizations among newborns and younger children, with the Centers for Disease Control and Prevention reporting between 58,000 and 80,000 hospitalizations per year among those under 5.

The four advisory members who voted against approving the vaccine said they were concerned about data suggesting the vaccine was linked to early deliveries in several low- and middle-income countries, though not in wealthier ones.

The committee chairperson, Dr. Hana El Sahly, a professor of Molecular Virology and Microbiology and Infectious Diseases at Baylor College of Medicine in Houston, criticized Pfizer for not clearing up safety concerns raised by earlier-stage trials in its most recent, larger one. “It was a big missed opportunity,” she said, after voting against the vaccine.

Assuming the vaccine receives final approval, federal officials will track its safety to ensure it is not triggering early deliveries. “I feel it’s unfair that we kicked the can down the road to the larger public,” El Sahly said.

Ten advisory committee experts voted in favor of approval, saying they felt the known risks of RSV outweighed their concerns about a small, potential risk from the vaccine.

RSV vaccines are on the way:Here’s what the CDC says about them.

In the fall, Pfizer said results from a Phase 3 clinical trial showed its vaccine protected infants when given to pregnant participants between 24 and 36 weeks of gestation. Through the first 90 days of a baby’s life, the vaccine was more than 81% effective at preventing severe illness. At 6 months, it remained nearly 70% effective.

The most common side effects reported in pregnant participants were mild to moderate and included fatigue, headache, muscle pain and pain at the injection site.

Of the roughly 7,400 participants who were enrolled in the trial, about 5.6% of infants were born premature, which the CDC says is on par with national preterm birth rates. A preterm birth is when a baby is born before 37 weeks.

Trial data also showed low birth weight was reported in 5.1% of infants whose mothers received the vaccine and 4.4% of infants whose mothers did not. About 18 fetal deaths were reported in the study, 10 in the vaccine group and eight in the placebo group, but the FDA agreed with investigators they were unrelated to the vaccine.

The advisory recommendation to approve the maternal shot comes weeks after the FDA approved the first RSV vaccine in the world. The shot was developed by GSK and approved for adults 60 and older.

Other RSV vaccines in the works

There are several RSV vaccines and treatments under review by regulatory agencies. Others include:

  • Sanofi’s monoclonal antibody for infants and toddlers: A monoclonal antibody from Sanofi and AstraZeneca, called nirsevimab, helps prevent RSV lower respiratory tract disease in newborns and infants entering or during their first RSV season. If approved, it would be the second monoclonal antibody on the market for infants. 
  • Pfizer’s vaccine for older adults: This vaccine candidate is under the same name as the maternal vaccine, RSVpreF. Pfizer data found its vaccine was more than 85% effective at preventing RSV-associated lower respiratory tract illness in older adults.

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

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