It's official: flu season is here. But experts say it's not too late to get a flu shot - your best protection against winter's wiliest virus.

"This year's vaccine appears to be right on target with the circulating virus," said Dr. William Schaffner, chair of preventive medicine at Vanderbilt University Medical Center in Nashville, Tenn. "Treat it as a holiday gift to yourself and everyone around you. Don't be a Grinch by spreading the flu."

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Flu season arrived early this year. And according to the U.S. Centers for Disease Control and Prevention, it could be a doozy.

"We're seeing the beginning of the uptick start at least a month before we'd generally see it," said the CDC director, Dr. Thomas Frieden. "It looks like it's shaping up to be a bad flu season."

Holiday parties and crowded cross-country travel give the flu an easy ticket to spread, according to Schaffner.

"There are a lot of interactions within your breathing zone," he said, referring to the three-foot radius around your mouth. "Those are all ideal circumstances for viral transmission."

Click here to see how to stay healthy during holiday travel.

While "avoiding coughers and sneezers" can help reduce your risk, flu symptoms can take days to appear. That means seemingly healthy friends and coworkers could be unwittingly exposing you to the flu.

"It 's not too late to get a flu shot," said Schaffner, who warned that flu season will likely extend through February or March. "Please don't doddle. Don't leave it to the last minute like a late Christmas eve shopping trip."

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If you do come down with flu symptoms, stay home and rest, Schaffner said.

"Don't go to holiday parties, don't go to work," he said. "You'll only expose all your friends, relatives and coworkers."