The United States appears to be in the midst of an unusually severe flu season, officials at the federal Centers for Disease Control and Prevention said Friday.

The flu season started early, which is never a good sign, and the flu is already widespread throughout the country, the CDC's latest report shows. Half of states are reporting especially intense flu activity.

"We are currently in the midst of a very active flu season with much of the nation experiencing widespread and intense activity," CDC Director Brenda Fitzgerald told reporters during a briefing.

Based on the latest available data, the United States could be experiencing one of the most severe flu seasons in years, possibly similar to the severe 2014-2015 flu season, officials say.

"Flu is everywhere in the U.S. right now. There's lots of flu in lots of places," says Dan Jernigan, director of CDC's influenza division.

Officials cautioned, however, that the flu is very unpredictable. So there's a chance the season could slow down quickly or end early, which could end up making it a more normal flu season.

But the most recent data show that the proportion of people rushing to their doctors to get treated for the flu has already hit 5.8 percent, which is as high as that number gets during the peak of a really bad flu season, the CDC says.

In addition, the rate at which Americans are being hospitalized for the flu almost doubled in the last week, to 22.7 for every 100,000 hospitalizations, according to the CDC.

Those are two of the key ways the CDC monitors the severity of a flu season.

So far, 20 children have died from the flu, compared to a total of 101 last season.

During the 2014-2015 flu season, 40 million Americans got the flu, 19 million people went to the doctor to get treated for the flu, and 970,000 people were hospitalized.

Officials, cautioned, however, that the hospitalization rate for the flu so far this year is slightly below the 2014-2015 rate.

The main reason the flu appears to be so severe is that it's a strain known as H3N2. That strain tends to make more people sick, and the people who get the flu tend to get sicker. It's especially dangerous for children and the elderly.

"When H3N2 is prominent, we tend to have a season with far more hospitalizations and deaths," Fitzgerald says.

To make matters worse, the vaccine may only be about 30 percent effective against that strain. That's better than the 10 percent effectiveness reported in Australia, which has its flu season before the United States does and often predicts what will happen in this country.

Nevertheless, health officials are urging people to get vaccinated. Any protection is better than none. And the vaccine may end up being more effective, especially if other strains of the flu become more common. The vaccine is more effective against those other strains. The vaccine can also lessen the severity of illness in people who get sick.

The flu season may be peaking in this country, but it could continue for many more weeks. So even though it takes two weeks for the vaccine to start protecting people after they get vaccinated, it's still worthwhile to get vaccinated, they say.

"While our flu vaccine is far from perfect, it is still the best defense we have," Fitzgerald says.

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