By Stephanie Stahl

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PHILADELPHIA (CBS) – After a relatively slow start to flu season, influenza activity is now widespread in nearly half of the United States. Last year was especially bad, as an estimated 80,000 people died from flu complications.

It’s been less severe so far this year, but federal health officials say they’re now seeing sharp increases in flu activity nationwide.

New Jersey has been especially hit hard with flu cases now high around the entire state.

The CDC says the number of states experiencing widespread flu activity has now doubled to 24, that includes Pennsylvania and Delaware.

The dominating virus this flu season is H1N1, which tends to impact young healthy adults and children.

Thirteen children have died from the flu so far this season.

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Federal health officials say it’s still not too late to get a flu shot.

“It can prevent you from getting sick, and even if you do get sick with influenza, it can prevent you from having to go into the hospital. Among hospitalizations so far this year, the highest rates that we are seeing are in those who are under age 5,” said Dr. Daniel Jernigan.

In this area, Pennsylvania has more than 6,400 positive flu cases, New Jersey has 439 and Delaware has 461.

That’s just confirmed tests. Officials say there are many, many more people sick with influenza.

“We actually work with a number of infectious disease modelers and they are forecasting when they think the peak would be and about 75 percent of those forecasts have the peak in January,” said Jernigan. “But we don’t know if that will be the case.”

Although flu cases are climbing, the numbers are still well behind this time last year, when the nation was in the midst of one of the most severe flu seasons on record. It was the deadliest in 40 years when less than half of Americans got vaccinated.

The CDC says early estimates show more people are being vaccinated this year, which could be one reason why this flu season isn’t as bad as last year, but that could change.

Stephanie Stahl