Credit: Courtesy John Sullivan

A lot of kids must sit on Santa's lap before he can hop in his sleigh on Christmas Eve, but Santa has to be extra careful during flu season if he wants to stay healthy into the New Year.

John Sullivan, a professional Santa Claus in Chicago, said he never turns down a child, even if the child's nose is runny.

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"I'll see him. I'll talk to him," Sullivan said. "That's just a risk that frankly comes with the job … Santa can't go around wearing a surgical mask!"

Since children actually exhale more flu virus than adults because their immune systems are immature, Santa and other people who work with children are at greater risk for coming down with the flu, said Dr. William Schaffner, chairman of preventative medicine at Vanderbilt University in Tennessee.

"Of course, Santa is leaning over the child and listening carefully. He's in the breathing zone of all these children," Schaffner said. "They come into very close contact with a myriad of children, and children are the great distributor of respiratory viruses."

Not only do children exhale more of the virus in each breath than adults do, but they also exhale it longer: 24 hours before they start feeling sick until after they feel better.

"It is likely because children are experiencing these viruses probably for the first time, and that their immune systems are not trained to combat the viruses and shut down the virus production mechanism quickly," Schaffner said.

Schaffner said it's important for professional Santa performers like Sullivan to get their flu shots, keep up their fluids and get enough sleep and exercise during the holiday season so that their bodies can fight the flu if they come in contact with it.

Sullivan has been Santa Claus every holiday season for more than two decades, and he never misses a flu shot, he said. He started in malls and now does private events at homes, offices and daycares.

"A lot of times when you pick up a baby, you can feel in their lungs that there's congestion," he said. "I'll tell the parent the baby has cold … Frankly, if I'm Santa, I never reject a child."

He said he's gotten mild colds, but nothing serious, and he's always mindful to avoid getting other people sick if he's not feeling well.

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Near Orlando, Greg Thompson runs The Santa Company, which has seven Santas, including Thompson himself, who has been dressing as Santa since he was 14. ("I'd discovered Santa's secret, so I decided I wanted to be him.") That first year, Thompson was 129 lbs., so his grandmother helped him stuff a pillow under his puffy jacket to complete the costume.

Although Thompson's size may have been a problem, the flu wasn't, he said. In fact, The Santa Company hasn't had anyone call out sick since it was founded in 1999.

"We have not had it happen yet - knock on wood - but if someone were to come in and say, 'Greg, I'm just sick and I can't come in,' we'd make sure to have a Santa for him," Thompson said. "We're more concerned about people bringing their kids to us. If a kid is obviously sick, you can look at him and tell, sometimes."

Of the 80 appearances The Santa Company does each year, Thompson does about a quarter of them. When a child approaches Thompson-as-Santa with a runny nose and red eyes, Thompson said he will ask the child to sit down in front of him instead of on his lap.

"I'll be happy to speak with him," he said.

Thompson added that his Santas always wear clean gloves as part of the classic red suit with white trim, and they cough only into their elbows.

But Schaffner said gloves can quickly become contaminated, and probably don't offer much protection against the virus as Santa touches a child and strokes his beard or touches his nose. Even surgeons are taught to wash their hands after they remove gloves, he said.

"They are at risk. There's no doubt about it," Schaffner said. "But maybe Santa's beard and mustache can act like a filter and keep the virus out," he joked with a laugh.

Santa is magical, after all.