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Pregnant women can now be vaccinated to prevent complications of RSV in infants. What to know about the FDA approval.

Pregnant women who received the RSV vaccine had infants who were protected from serious complications of the virus, according to a new study. (Getty Images)
Pregnant women who received the RSV vaccine had infants who were protected from serious complications of the virus, according to a new study. (Getty Images)

The Food and Drug Administration (FDA) has approved Abrysvo, the first vaccine approved for use in pregnant individuals to prevent lower respiratory tract disease (LRTD) and severe LRTD caused by respiratory syncytial virus (RSV) in infants up to 6 months old. The vaccine's approval comes a month after the FDA approved Beyfortus, a new drug to prevent RSV in babies and toddlers. In May, the federal agency approved Abrysvo to prevent LRTD caused by RSV in people 60 and older.

Pregnant women can now receive the vaccine, which is administered as a single-dose injection, between 32 and 36 weeks into their pregnancy.

“This approval provides an option for health care providers and pregnant individuals to protect infants from this potentially life-threatening disease," Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, says in a release.

In May, an FDA advisory panel voted in favor of the vaccine. In April, a study published in the New England Journal of Medicine found that pregnant women who received the then-unnamed vaccine had babies who were protected from serious complications of the virus. The study gave 3,682 women the vaccine and 3,676 a placebo. The researchers found that six babies born to women in the vaccine group had severe LRTD within 90 days after they were born compared to 33 infants in the placebo group, indicating that the vaccine had a nearly 82% efficacy rate against severe LRTD.

Efficacy waned over time: Six months after birth, the vaccine was 69% effective.

There were no major safety concerns with the vaccine, although 5.6% of pregnancies in the vaccine group ended in premature delivery compared to 4.7% in the placebo group. (Advisory committee members said the difference is not statistically significant — meaning it's not big enough that it's clear that the vaccine caused the difference in numbers.)

According to the FDA, the most commonly reported side effects were pain at the injection site, headache, muscle pain and nausea. The agency also noted that 1.8% of pregnant individuals who received Abrysvo experienced pre-eclampsia, compared to 1.4% of those who received the placebo. Abrysvo recipients also saw a higher rate of low birth weight and jaundice in their infants, compared to the placebo group.

Why is the vaccine important?

Speaking to Yahoo Life ahead of the Abrysvo approval, doctors said they were encouraged by the clinical trials, especially after the rough RSV season the country faced this past winter.

"It's critically important to have this vaccine in the pediatric age group," Dr. Thomas Russo, a professor and chief of infectious diseases at the University at Buffalo in New York, tells Yahoo Life. "The zero to 6-month age group — along with older adults — are at the greatest risk for severe disease and serious outcomes from RSV."

RSV is the most common reason for infant hospitalizations in the U.S. and a "huge driver of pneumonia," Dr. Mike Tsimis, an OB-GYN and maternal-fetal medicine physician at Corewell Health, tells Yahoo Life. In children under 5, RSV leads to 2.1 million outpatient visits, up to 80,000 hospitalizations and up to 300 deaths in the U.S. each year, according to data from the Centers for Disease Control and Prevention. "To date, there is no childhood vaccine for RSV," Tsimis points out.

How does the RSV vaccine work?

The reason the shot is given to pregnant women and not the babies themselves is because the newborn immune system is so immature, Russo explains. "The idea is that we'll vaccinate pregnant women, and they'll make the antibodies that will cross the placenta and offer the baby protection for the first few months of life," Dr. William Schaffner, an infectious disease specialist and professor of medicine at the Vanderbilt University School of Medicine, tells Yahoo Life.

The vaccine is given as a single dose during pregnancy and is intended to help protect the baby for the first six months after birth.

Schaffner says that an RSV vaccine for pregnant women may be available as early as the fall.

He adds that an RSV vaccine for pregnant women is definitely needed. "RSV is the last of the important seasonal viruses for which we don't have a vaccine," he says. "We have one for flu and COVID, and RSV is one that causes an awful lot of illness."

This article was originally published on May 22, 2023 and has been updated.

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