By Stephanie Stahl

PHILADELPHIA (CBS) — Federal health officials say the U.S. winter flu season is off to its earliest start in more than 15 years. New numbers released Friday by the Centers for Disease Control and Prevention show the flu is spreading fast.

It’s not in our area in a big way yet, but the Pennsylvania Health Department says it has 2,667 confirmed cases.

Flu season is arriving with a bang and it’s early. Southern states are the hardest hit right now and flu B viruses are dominating.

“That’s a bit odd because the influenza B’s are usually more active at the end of the season. Here we are at the beginning. We don’t know why that is but it’s noteworthy because influenza B’s like to affect children,” said Dr. William Schaffner, of Vanderbilt University Medical Center.

So far, the CDC estimates that there have been as many as 2.5 million flu illnesses, 29,000 hospitalizations and 2,400 deaths nationwide.

Twelve states and Puerto Rico are now experiencing high influenza-like illness.

Doctors are urging if you haven’t been vaccinated, now is the time to get your flu shot.

“Please run, do not walk. Get your vaccine as quickly as possible,” Schaffner said. “You know it takes one to two weeks for your body to make your full protection. We all know the flu vaccine isn’t a perfect vaccine but remember this even if you get vaccinated for the flu, you are much less likely to have the severe complications like pneumonia, hospitalization and dying.”

While some are concerned that an early start could mean we’re in for a tough season, experts say it’s too early to make any predictions.

Health officials say this year’s vaccine has been reformulated to include more of the B-strain that’s starting to circulate. By comparison, last flu season started off as a mild one but turned out to be the longest in 10 years.

Stephanie Stahl