Transcript for Flu Season Sees a Dramatic Spike
Tracking the flu. Which is making a strong comeback after a slow start. Just last week, six states reported a high level of flu. But tonight, the map stretches to 20 states. And abc's a dealy roy has the story. Reporter: The flu is now hitting hard and spreading fast. It first took off in the south. With texas and mississippi getting hit before thanksgiving. Now into the southeast and the west. The cdc says the dominant strain so far this season? The h1n1 virus, which hits young and middle aged harder than older people, who may have developed some immunity after facing a similar strain in the 1940s AND '50s. The message tonight, it's not too late to get a flu shot. Officials say it can reduce your chances of getting the virus by 50 to 70%. The best and quiest protection, against what is now a fast moving enemy. Aditi roy, abc news, san francisco.
This transcript has been automatically generated and may not be 100% accurate.