Respiratory syncytial virus – better known by the acronym RSV – is rising in some southeastern U.S. states, the Centers for Disease Control and Prevention warned Tuesday, signaling the virus could begin spreading widely nationwide soon.

RSV causes cold-like symptoms for most people, but can be scary for infants, young children, elderly people, and those with weakened immune systems. The virus kills between 100 and 300 children under 5 and as many as 10,000 people over 65 annually, according to CDC estimates.

Other than a few atypical years during the COVID-19 pandemic, the RSV season usually starts in fall and peaks in winter. The virus also has a history of starting to spread in Florida, before spreading to other southeastern states, then eventually northward and westward.

That appears to be the case again this year. In recent weeks more patients have been testing positive for the virus in Florida and Georgia, the CDC said in an alert issued Tuesday.

“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 CDC said.

But doctors will have new tools to fight RSV this season. Last month, U.S. regulators approved the first RSV vaccine for pregnant women so their babies will be born with protection against the respiratory infection.

The Food and Drug Administration cleared Pfizer’s maternal vaccination to guard against a severe case of RSV when babies are most vulnerable — from birth through 6 months of age. The next step is for the CDC to issue recommendations for using the vaccine, named Abrysvo, during pregnancy.

Vaccinations for older adults, also at high risk, are getting underway this fall using the same Pfizer shot plus another from competitor GSK.

The Associated Press contributed to this report.