Respiratory illness activity is on the rise. Here's what parents need to know about RSV.

Cases of respiratory syncytial virus (RSV) exploded in the U.S. last winter, sickening large numbers of children and even sending some to the hospital. While RSV wasn’t a new illness, many parents heard about it for the first time last year.

According to the Centers for Disease Control and Prevention, RSV activity "remains elevated" across the country, though some areas have seen decreases in cases. The CDC also noted that hospitalization rates are up, especially among young kids and older adults. And though adults aged 60 and up are eligible to receive a new RSV vaccine, only 17.4% of them have done so.

But what is RSV exactly, and what kind of treatment options are available? Doctors break it down.

What is RSV?

RSV, which typically starts in the fall and peaks in the winter, is an extremely common childhood illness. Here’s what you need to know about this virus:

• RSV is one of the most common causes of childhood illness, according to the CDC. It’s also the most common cause of hospitalization in infants.

• Nearly all children will have been infected by RSV by the time they turn 2.

• It was first discovered in 1956.

• An estimated 58,000 to 80,000 children younger than age 5 are hospitalized in the U.S. each year due to RSV infection.

• Most children who have RSV experience only cold-like symptoms, the CDC says, but some can develop serious complications like bronchiolitis (an inflammation of the small airways in the lung) and pneumonia (an infection of the lungs).

RSV symptoms in kids

RSV usually causes cold-like symptoms in kids, according to the American Academy of Pediatrics (AAP), including:

• Fever (temperature of 100.4 degrees Fahrenheit or higher)

• Cough (dry- or wet-sounding)

• Congestion

• Runny nose

• Sneezing

• Fussiness

• Poor feeding

If a child develops bronchiolitis, the AAP says these additional symptoms may emerge:

• Fast breathing

• Flaring of the nostrils and head bobbing with breathing

• Rhythmic grunting during breathing

• Belly breathing, tugging between the ribs and/or the lower neck

• Wheezing

What does the latest data on RSV say?

A new study published in the journal JAMA Network Open analyzed data from 600 infants across 39 hospitals in the U.S. who needed intensive care for an RSV infection in 2022 and found that most were delivered at full term and were previously healthy. Children who were less than 3 months old and those who were born prematurely were at the highest risk of intubation, the researchers found.

While RSV can infect anyone, doctors typically warn that children who are born premature or who have underlying health conditions are the most at risk for serious complications from the virus. “While we focus a lot on high-risk individuals, healthy individuals could also get severe disease and land in the hospital,” Dr. Thomas Russo, a professor and chief of infectious diseases at the University at Buffalo in New York, tells Yahoo Life.

“The majority of infants in the U.S. are born at term — 89.5% in 2022 — so although preterm infants are at higher risk to get very ill from RSV, term newborns are still a very high-risk group,” Dr. Ann Anderson Berry, executive director of the Child Health Research Institute, tells Yahoo Life. “Given the large number of them, they will still make up the largest group of patients hospitalized with this condition.”

New RSV treatment options

In July, the Food and Drug Administration approved a new RSV drug for babies and children. Called Beyfortus (nirsevimab), it’s a preventive treatment that delivers long-acting antibodies via a process called passive immunity, Russo explains. Beyfortus doesn’t require the activation of the immune system to develop antibodies to RSV, according to Sanofi, which helped create the drug.

The CDC recommends one dose of Beyfortus for all infants under the age of 8 months who were born during or entering their first RSV season, as well as for those children between the ages of 8 and 19 months who are at increased risk of severe RSV disease and are entering their second RSV season.

In August, the FDA approved the first RSV vaccine for pregnant women. A study of nearly 7,400 pregnant women found that it was 82% effective at preventing lower respiratory tract disease (LRTD) caused by RSV during the first three months of their babies' lives. At age 6 months, it was still 69% protective against severe complications of the virus. Women can take the single-shot vaccine, named Abrysvo, between 32 and 36 weeks into their pregnancy.

In September, an advisory panel for the CDC officially issued its recommendation that Abrysvo be given during weeks 32 to 36 of pregnancy.

What’s next for RSV?

Doctors say they’re not entirely sure what to expect during the upcoming RSV season. “The seasonality of RSV is somewhat uncertain this year, as the 2022-23 season was markedly different than pre-pandemic years,” Anderson Berry says.

Russo agrees. “Given that we had a really bad RSV season last year, we’ve likely developed some immunity,” he says. ”Hopefully this season won’t be as severe, but RSV isn’t going anywhere.”

Speaking to Yahoo Life in December, CDC director Mandy Cohen addressed elevated RSV, COVID and flu activity. “We expected to see more viruses, we expected to see more COVID and flu and RSV, and that’s exactly what we’re seeing,” Cohen said. “I think we are still too early in the season to really compare to last year to characterize whether this is a bad season or not. What I’d say [is that] right now is pretty typical.”

While there are new tools to help lower the risk of severe RSV, Anderson Berry says parents should still be mindful that RSV will be circulating this winter and is a risk to newborns and infants. “Even with new therapies, minimizing risk by simple infection-control measures such as handwashing, staying home when ill and minimizing newborns’ contact with large groups during cold and flu season is still best practice,” she says.

This article was originally published on Aug. 16, 2023 and has been updated.