LEXINGTON, Ky. (WKYT/CBS) - Flu season has started early in the United States. The Centers for Disease Control says this is the earliest flu season in a decade.

Doctors say flu season normally peaks in mid to late February. But hospitals in Chicago are already so overrun with flu cases, they've had to turn patients away from emergency rooms.

"We don't have a great explanation for why it started so early this year," said Dr. Allison Bartlett, Infectious Disease Expert at the University of Chicago Medicine.

Kentucky is one of 41 states reporting widespread cases of the flu. So far, at least 18 deaths have been blamed on the virus nationwide. Each year influenza deaths range from a low of 3,000 to as many as 50,000.

Only about 37% of Americans have received the flu vaccine this year. Experts at the Centers for Disease Control say the vaccine covers 91% of all strains analyzed this year. That's why experts say you should still get the flu vaccine.

"Even if it doesn't prevent the infection completely, it can definitely make the infection much less severe," Dr. Bartlett says.

"What we want people to realize is there's still plenty of time to get a flu shot. In Kentucky, the peak flu season isn't until late January, early February so, you're still quite a bit away from seeing those numbers start to sky rocket," said Kevin Hall, with the Fayette County Health Department.

Doctors say in addition to getting the flu vaccine, you should wash your hands frequently to keep from getting sick.