The Centers for Disease Control and Prevention has declared a national flu epidemic.

Health officials are expected to release updated numbers on flu cases today.

Health officials say 15 children have died from the illness and 36 states have seen large numbers of illness.

Doctors say this year's flu vaccine is only about 40 to 50 percent effective because the vaccine doesn't protect from the current strain.

They recommend that people still get vaccinated as a precaution.