The flu epidemic has hit a milestone that hasn't happened in over a decade

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• Doctors at the Centers for Disease Control and Prevention (CDC) say they're seeing "widespread" instances of the flu in 49 states.
• It's the first time that many states have been slammed by the flu at the same time in over a decade.
• Some evidence suggests that the worst of the flu season is upon us, and that the flu shot will be better at protecting more late-season cases this year.

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Flu season arrived early in the US this year, and it's been deadly. To make matters worse, the current vaccine isn't working very well against one of the most common strains of the virus .

"This year's influenza season is proving particularly difficult" CDC Deputy Director Anne Schuchat said during a briefing on Tuesday.

Perhaps most the most unusual thing about this year's flu, experts say, is that it's hitting almost everyone at the same time.