Regulators with the U.S. Food and Drug Administration (FDA) on Aug. 21 approved the first vaccine to be taken by pregnant women to prevent respiratory syncytial virus (RSV) infections in babies and toddlers.

Pfizer’s Abrysvo vaccine, a first-of-its-kind single-dose injection administered into the muscle, was approved for use at 32 through 36 weeks of pregnancy.

According to the FDA, pregnant women who receive immunity from the shot will pass that immunity along to their unborn baby before birth, thus protecting them from lower respiratory tract disease (LRTD) and severe LRTD caused by RSV until at least the age of 6 months.

However, the virus is especially common in children, most of whom would have had an RSV infection by the time they reach two years of age.

While it often causes cold-like symptoms in infants and young children, as it does in adults, it can also lead to serious LRTD such as pneumonia and bronchiolitis (swelling of the small airway passages in the lungs).

That study was conducted among approximately 3,500 pregnant women. For pregnant women in the study who were 32 to 36 weeks pregnant, Abrysvo led to a 34.7 percent reduction in LRTD risk and a 91.1 percent reduction in severe LRTD risk within 90 days after birth, according to the FDA.

However, certain side effects were reported among pregnant women who received the shot, including pain at the injection site, headache, muscle pain, and nausea, the FDA said.

Additionally, although not commonly reported, a dangerous hypertensive disorder, known as pre-eclampsia—a serious blood pressure condition that sometimes develops during pregnancy—occurred in 1.8 percent of pregnant individuals who received Abrysvo compared to 1.4 percent of pregnant individuals who received a placebo, the FDA said.

Pre-eclampsia can be life-threatening to both the mother and the baby.

“In the safety studies, low birth weight and jaundice in infants occurred at a higher rate in the pregnant Abrysvo recipients compared to pregnant placebo recipients,” the FDA said.

Still, Annaliesa Anderson, senior vice president and chief scientific officer of vaccine research and development at Pfizer touted the approval of Abrysvo as the “first and only maternal immunization” of its kind, calling it a “significant milestone for the scientific community and for public health.”

“We are incredibly grateful to the clinical trial participants and study investigator teams around the world, as well as our Pfizer colleagues, for their commitment to making this vaccine available. Today, a long-sought-after goal to deliver a maternal vaccine that will help protect infants six months of age or younger—when they are at greatest risk of possible serious consequences from RSV—has been achieved,” Ms. Anderson said.