'October is the ideal time to get vaccinated': Flu season is kicking off early, experts say

Flu season is off to an early start in some parts of the U.S., data shows.

In a typical year, U.S. flu activity starts building in late fall — typically in October or November — and peaks between December and February.

This year, flu activity is currently low but rising nationwide: During the week ending Sept.

26, 3.4% of respiratory samples tested by clinical labs were positive for flu, according to Centers for Disease Control and Prevention (CDC) data .

That's about seven times the rate that was seen at the same point last year.

About 0.5% of samples tested positive during the week ending Sept.

27, 2025.

"This particular year, it appears to be starting early — like right now," Dr.

William Schaffner , a professor of preventive medicine and infectious diseases at Vanderbilt Health in Tennessee, told Live Science.

Patients at clinics in his area are already testing positive for flu, he said.

The early uptick in flu is mostly unfolding in Western states, including Washington, California and Arizona .

In Washington, for example, the share of emergency department visits diagnosed as flu climbed from 0.25% in the week ending Aug.

29 to 1.34% in the week ending Oct.

3, according to CDC emergency department data .