A strain of the influenza is circulating not covered by this year's vaccination.
The State Health Department said the type-b strain is not currently widespread. However, people who got the flu vaccine could still get sick if they come into contact with a person infected carrying this flu strain.
The health department also noted flu activity, as measured by sentinel physician reporting and laboratory testing in Oklahoma, was elevated to widespread for the week ending February 2.
Yet health officials are still recommending the flu shot.
"There are other flu viruses, strains, that are in that shot. And just because you get one doesn't mean you can't get another kind," said Janice Sheehan from the Tulsa County Health Department.
The good news is health officials said the type-b flu tends to have milder symptoms than type-a strains.