Flu season is upon us, and it's hitting North Texas pretty hard.

Five deaths caused by influenza have been reported in Dallas County as of Jan. 2, according to Dallas County Health and Human Services.

About 20 percent of influenza tests in Dallas County hospitals came back positive before Dec. 23, the DCHHS said in its report, which is 5.5 percent higher than the national average.

Tarrant County also reported an increase in positive flu cases through Dec. 23. The percentage of rapid flu test positives nearly doubled in one week.

At least nine deaths have been reported nationwide this flu season. Thirty-six states reported widespread flu activity, the Centers for Disease Control and Prevention said.

"It's just one of those years where the CDC is seeing that this strain of flu is only somewhat covered by the vaccine that was given this year," said Jennifer Radtke, manager for infection prevention at the University of Tennessee Medical Center in Knoxville. "They're seeing that it's anywhere from 10% to 33% effective, so any time there's a mismatch between the vaccine and the circulating strain of the flu, you're going to see more cases."

February is usually the peak time for flu season.

Symptoms include a fever, cough or sore throat, aches, chills, and fatigue.

Go here for more information on how you can protect yourself.