Airplanes are notoriously germy places. Studies have shown that airplane bathrooms harbor a number of different types of bacteria and viruses, and the recirculated air in planes can also contain many infectious agents. Germs also lurk on tray tables and on seats and seat backs.
"If you're in a plane, wipe down seats, seat backs and tray tables," said Bernstein. Travelers should also, as always, wash their hands whenever possible.
A 2009 study by the U.S. Centers for Disease Control and Prevention found that passengers on two lengthy flights into Australia were at increased risk for getting a flu-like illness after the flight if they sat up to two rows away from a person who had flu symptoms before the flight. They were at even higher risk if a symptomatic passenger sat within two seats in front, behind or to the side.
While it may be difficult to control who sits in nearby seats or rows, if a person is sneezing or coughing, try to stay away from that person and disinfect surfaces and hands regularly.
"Also, don't touch your eyes, mouth or nose, since there are only so many times you may be able to wash your hands," said Perskin.
Spreading germs is a two-way street, so people who may be coughing or sneezing should be careful to avoid coughing or sneezing into other people's faces and should use tissues or hold their mouths when possible. They should also, of course, wash their hands.
Proper nutrition and physical activity are important all year round, but especially during the holidays. People may neglect these needs because of bad weather or other obligations, but they are vital to staying healthy.
"Eat a healthy diet and exercise -- those are the best preventive activities along with not smoking," said Perskin. "Your immune system will be healthier and that will help fight off infection."
"Even though it's December, it's not too late to get a flu shot. Flu season goes through early spring," said Bernstein.
"This is the prime time for influenza," said Gardner. "When peole are in enclosed spaces in cold environments, the passage of viruses -- especially the flu virus -- is much greater than in wide open spaces in the summer."
Perskin also suggests getting vaccinated against other disease, such as whooping cough, or pertussis.
Although it may seem inconvenient to worry about flu shots on top of everything else, the alternative could be a lot worse.
"It would be an enormous waste of time if, because of not getting vaccinated, someone spent five days in bed with a fever and just felt crummy," Gardner said.
A version of this story previously appeared on ABCNews.com.