The Food and Drug Administration has approved the first RSV vaccine for expectant mothers aimed at protecting their newborn babies.

Given during the third trimester of pregnancy, Pfizer's new shot – Abrysvo – protects infants from lower respiratory tract disease caused by RSV, or respiratory syncytial virus, through their first six months of life.

RSV is a common respiratory virus that usually results in mild symptoms, but can be serious in infants, young children and older adults. Each year, up to 80,000 children under 5 are hospitalized with RSV, according to the Centers for Disease Control and Prevention. That makes it the leading cause of hospitalization among infants.

"RSV has plagued the infant population of not just the United States but the world for years," says Dr. Scott Roberts, assistant professor of infectious diseases at Yale School of Medicine.

In May, an FDA committee of advisors voted unanimously in favor of the shot's efficacy. The FDA usually follows suit and approves drugs the committee votes in favor of, but not always.

A study of 7,400 women in 18 countries found the vaccine was 82% effective at preventing severe disease in infants during their first three months of life and 70% effective in the first six months.

"There have been attempts at developing both vaccines and therapeutics against RSV that have failed for decades," Roberts says. "A lot of us in the medical community are facing the winter ahead with some optimism and enthusiasm that we now have several options that are coming down the pipeline."

Last year, RSV emerged earlier than usual and overwhelmed many children's hospitals, showing how a bad season can strain the country's ability to care for severely ill children.

Dr. Eric Simoes, from the Children's Hospital Colorado, worked with Pfizer and has been working on RSV prevention for decades. He calls this approval fantastic news.

"My only hope is that we can get these vaccines not only in the U.S., but also to children in developing countries that need it the most," says Simoes.

So far this year, in states like Florida and Georgia, RSV activity has already begun, according to Force of Infection, the newsletter by Dr. Caitlin Rivers, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health.

The vaccine was originally approved in May for adults over 60. It's already available for the 2023-24 RSV season. Pfizer says it has been manufacturing the shot ahead of approval and expects to have enough supply to meet demand.

Roberts says he's especially optimistic because his family is expecting a baby in December during the typical peak of RSV season. Now, they'll have some options for protection.

"The thing about RSV is that it really hits healthy infants hard and generally, regardless of pre-existing condition, we have kids get admitted to the hospital with RSV disease and some die who are otherwise completely healthy," he says, "That really concerns me."