CDC issues warning RSV is on the rise in young children in Southeastern US

The increase may be the start of the RSV season nationally, says CDC.

The Centers for Disease Control and Prevention warned this week that cases of respiratory syncytial virus, or RSV, are rising among young children in some parts of the Southeastern United States.

Traditionally, RSV season begins in the fall and continues through the winter, similar to the flu and other respiratory viruses. However, RSV infections this time of year are much higher than usual, in Florida and Georgia, particularly.

Over the past four weeks, the three-week average of PCR test positivity for RSV in Florida has been above 5%, which exceeds the threshold of 3% typically seen at the start of the RSV season, the CDC said in a heath advisory.

In Georgia, RSV-linked hospitalizations among those under age 4 have risen from 2.0 per 100,000 for the week ending Aug. 5 to 7.0 per 100,000 for the week ending Aug. 19, the CDC said. What's more, the majority of those hospitalizations were among children less than a year old.

"Historically, such regional increases have predicted the beginning of RSV season nationally, with increased RSV activity spreading north and west over the following 2-3 months," the agency wrote in its advisory.

The CDC said it wants clinicians and caregivers to be aware of RSV because it can be particularly dangerous for babies, young children and older adults.

Last year, RSV also appeared earlier than usual, spiking in October before declining in November. At the time, experts told ABC News that this might have occurred because children were not exposed to potential infection between 2020 and 2022 due to lockdowns, or because they were born during the pandemic.

RSV symptoms typically appear between four and six days after infection and include fever, runny nose, sneezing, coughing, wheezing and a decrease in appetite, with the symptoms usually occurring in stages, according to the CDC.

An estimated 58,000 to 80,000 children under age 5 are hospitalized with the virus every year, as well as 60,000 to 160,000 people aged 65 and older, the CDC said.

Moreover, some infants and young children are at an even greater risk of severe illness from RSV, including those born prematurely, immunocompromised children and those suffering from congenital heart and lung diseases.

Between 100 and 300 children die every year from RSV, as do 6,000 to 10,000 senior citizens, according to the CDC.

However, this season there will be protection against RSV offered to many Americans for the first time ever. Firstly, adults over 60 will be able to get vaccinated. Similar to flu shots, the vaccines will be available at major pharmacy chains such as CVS, Rite Aid and Walgreens.

There's also a new RSV drug available this season. Called Beyfortus, it was recently approved for infants younger than eight months experiencing their first RSV season, with some high-risk infants eligible to receive a second shot the following year.

Beyfortus is a one-dose injected drug made of monoclonal antibodies, which are proteins manufactured in a lab that mimic antibodies the body naturally creates when fighting an infection. Though given as an intramuscular injection, Beyfortus works in a different mechanism than a vaccine to activate the immune system.

A third type of RSV treatment may also become available, an immunization that would be given during late pregnancy in the hopes of passing on protection to newborns. Approved by the Food and Drug Administration last month, it's currently awaiting CDC approval before becoming available.

ABC News' Dr. Evgeniya Jenny Rakitina contributed to this report.