Pfizer RSV Vaccine Effectively Protects Infants When Given To Pregnant People

This vaccine would be the first against the illness that hospitalizes an estimated 58,000 to 80,000 U.S. children under 5 each year.

Pregnant person getting a vaccine

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Parents of young children are acutely aware of a triple threat of respiratory viruses circulating as winter approaches: The flu, COVID-19, and respiratory syncytial virus (RSV).

Children ages six months and up are currently eligible for vaccines that provide strong protections against severe outcomes, including hospitalization and death, for the flu and COVID-19. Today, Pfizer announced it has enough data on the safety and efficacy of an RSV vaccine to protect infants. Pfizer plans to submit its data to the U.S. Food and Drug Administration (FDA) for approval by the end of this year.

RSV typically presents as flu-like symptoms, says Dr. Sarah Pachtman, MD, the associate director of maternal/fetal medicine, inpatient services at LIJ Medical Center.

Dr. Jennifer L. Lighter, MD, a pediatric infectious disease specialist with NYU Langone Health, adds that most children get the virus before they are two. But it can be risky to infants, premature babies, and children with heart and lung disease. Between 58,000 and 80,000 children under 5 are hospitalized with RSV each year, and 100 to 300 die, according to CDC estimates.

"We need a universal vaccine at this point because there is significant morbidity in the U.S. and worldwide," Dr. Lighter says. Pfizer believes they have an option. According to data released by the company on Tuesday, its RSV vaccine was 82% effective in preventing hospitalization in infants younger than 90 days old and 69% for babies under six months old when given to the person carrying them in utero.

The trial involved giving the vaccine to 7,400 pregnant people in their late second or third trimesters in 18 countries across the Northern and Southern Hemispheres. Dr. Pachtman compared it to the t-DAP vaccine, which is given to pregnant people in their third trimester and ultimately provides protection against whooping cough for the newborn until they can get their shot around eight weeks of life.

"We have other vaccines that we can give [people] during pregnancy that generate a robust immune response and transfer antibodies across the placenta to fetuses, and the babies are immune once they are born for a time," Dr. Patchtman says. "This news [from Pfizer] is very encouraging."

If approved, the vaccine would be the first of its kind to protect against RSV.

Currently, the most at-risk babies, including those with heart and lung diseases or born at 32 weeks of gestation or earlier, can receive monoclonal antibody treatment once per month. It reduces hospitalization for RSV by about 55%, but it's not widely available for all infants. In September, European Medicines Agency recommended a more straightforward treatment—a single-dose antibody designed for any infant. It can provide season-long protection, according to data from Sanofi.

Though all of this news is promising, it's unlikely to provide protections during this year's RSV season.

Dr. Pachtman says that parents can protect their at-risk infants and children by:

  • Washing hands and requiring anyone that comes in contact with them or their baby to do the same.
  • Requiring visitors to wear masks.
  • Asking people to stay home if they are not feeling well.

Dr. Pachtman also encourages people to protect the most vulnerable by staying home if they are sick–even if someone doesn't specifically make that request.

If someone suspects their child has RSV, there is a swap or blood test that can diagnose it. She suggests calling your pediatrician if you suspect your child has RSV and going to the emergency room if they are having trouble breathing.

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