(CBS) — The flu shot you received may not protect you from getting the flu.

There are several strains of the virus, making it important for you to get antiviral medication right away, when flu symptoms hit. CBS 2’s Suzanne Le Mignot explains.

Dr. Dino Rumoro, chairman of the Department of Emergency Medicine at Rush University Medical Center, heads a team that created the Guardian System in use at Rush and Rush Oak Park.  It tracks flu cases, in real-time.

“We’re in widespread influenza. We have widespread activity throughout the Chicagoland area,” Rumoro says.

The Centers for Disease Control and Prevention says the flu vaccine in use right now matches about half of the flu cases this year.  The director of the CDC, Dr. Tom Frieden, spoke by phone about the need to take antiviral medications, like Tamiflu, in the first 48 hours of flu symptoms.

“Treating early with these drugs can make the difference between having a milder illness or a very severe illness,” he says.

Dr. Rumoro says people should still be getting the vaccine, given that up to 40,000 people die each year from influenza.

“With that kind of mortality rate, with a disease that’s highly contagious, they should get the vaccine, because it’s safe and it is available,” Frieden says.

Those most at risk for the flu—children, the elderly, pregnant women—and those with chronic conditions, should seek treatment right away.  Don’t forget, one of the best way to avoid getting the flu is washing your hands.