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The U.S. may be entering another rough winter for flu, according to early data.

"The signs are, it could be a big season," says 

, who studies the flu at St. Jude Children's Research Hospital in Memphis. "The flu season might have a little bit of a punch to it this year."

The first clue to what may be in store is what influenza did during the Southern Hemisphere's winter. That often predicts what's coming for the Northern Hemisphere.

"They had some pretty decent flu activity in many parts of the Southern Hemisphere," Webby says. "It actually lasted for a longer period of time — the tail of the season went on for longer than typical."

And now, parts of the Northern Hemisphere, such as the United Kingdom, are being hit hard. That often foreshadows what's in store for the U.S.

Another clue is the Northern Hemisphere's dominant flu strain so far. It's an H3N2 flu virus, 

according to the Centers for Disease Control and Prevention

And H3N2 viruses "tend to be a little bit more problematic," Webby says. "When we have an H3N2 season, we tend to have a little bit more activity, a little bit more disease at the severe end of the spectrum."

The last major flu season dominated by H3N2 was 2016-2017.

In addition, a new H3N2 variant recently evolved and has become the dominant strain in the U.S.

"There is basically a new variant of influenza circulating that has mutated a little bit," says 

, an epidemiologist at Johns Hopkins. "And that means that it's just different enough from what your body or the vaccine may recognize that it can kind of get around those protections."

And she says the flu shot this year "may not be as good a match as if we hadn't seen this new variant."

That said, data from the U.K. indicates the vaccines still make a difference, Rivers says. In the U.K., the vaccines appear to be about 70 to 75 percent protective against hospitalization in children and about 30 to 40 percent protective against hospitalization in adults.

So Rivers and others are urging anyone who hasn't already gotten a flu shot to get one.

"Definitely get it as soon as possible. Because activity is low right now. But it is increasing. And it will continue to increase straight through until we hit peak, which is usually around the holiday season. There's no sense in waiting when we are barreling into flu season," Rivers says.

It takes about two weeks for immunity to kick in. And people don't want to catch or spread the flu over Thanksgiving. The flu kills between roughly 12,000 and 52,000 people in the U.S. every winter.

"I do have concerns that uptake of both the influenza and the annual COVID vaccine won't be as high this year as it had been in previous years," Rivers said. She is concerned by rhetoric coming from federal health officials questioning "whether vaccines are safe and effective."

"We know that they are," she says. "And they are important for protecting against severe illness. So it's really important that people go out and get them this year."

In a written statement to NPR, a Health and Human Services spokesperson said: "It is too early to know what viruses will spread this season, in what proportion, and how well the vaccine will work in the United States."

The statement added: "The decision to vaccinate is a personal one. Individuals should speak to their healthcare provider on the risks and benefits of a vaccine."

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Rob Stein

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With a new flu virus variant circulating, scientists fear more sickness this winter. The vaccine may be slightly less effective, but doctors still urge getting one ASAP.

Flu season could be nasty this winter

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