MIAMI (CBSMiami) — Flu season is now underway for most of the United States including Florida. It’s the earliest start in more than 15 years. Federal health officials have released their first case estimates.

The southern states are the hardest hit right now and flu B viruses are dominating.

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Dr. William Schaffner from Vanderbilt University Medical Center says, “That’s a bit odd because the influenza Bs 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 Bs like to affect children.”

The CDC estimates, so far this season, there have been as many as 2.5 million flu illnesses, 29,000 hospitalizations, and 2,400 deaths nationwide. Five of those deaths were children, according to the CDC.

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

The states are: Alabama, Georgia, Louisiana, Minnesota, Mississippi, Nebraska, Nevada, New Mexico, South Carolina, Tennessee, Texas, and Washington.

In Florida, flu activity is increasing and remained “above levels observed at this time in previous seasons,” according to the Florida Department of Health. Flu activity is also “particularly elevated in children for this time in the season.”

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

“Please run, do not walk,” says Dr. Schaffner. He adds “Get your vaccine as quickly as possible. You know it takes 10 days to 2 weeks for your body to make your full protection. We all know that the influenza vaccine is not a perfect vaccine. But remember this, even if you get vaccinated and get the flu, you’re much less likely to have the severe complications, 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 it’s possible the flu season could also peak much earlier than normal.

Last flu season started off as a mild one but turned out to be the longest in 10 years. It ended with around 49,000 flu-related deaths and 590,000 hospitalizations, according to preliminary estimates.

It was bad, but not as bad as the one before it, when flu caused an estimated 61,000 deaths and 810,000 hospitalizations.

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In both of the previous two flu seasons, the flu vaccine performed poorly against the nasty predominant virus. It’s too early to say how well the vaccine is performing right now, say experts.