[Updated January 2015, with additional reporting and writing by Teresa Bitler]

Up to 20 percent of the population gets the flu and the average adult typically gets at least one cold every year, which means there’s a definite possibility the person you end up sitting next to on your next flight could be contagious with one or the other. Here are some ways you can protect yourself and avoid getting a cold, the flu, or worse when you’re seatmate is sick.

Airplane Air 101
First things first. Cramped for space as passengers might be, an airplane’s air circulation is far superior to, say, your office’s. Fresh air from outside the aircraft is pumped in every few minutes -- up to 30 times per hour, in fact, compared to the office average of 12 -- through sterilizing filters comparable to those used in hospital operating rooms. Air is also ventilated within three- to seven-row sections, meaning you’re only “sharing” the air with people in that radius.

Getting Back to Flu Prevention Basics
But what if you’re sitting right next to someone who does appear to be sick? Requesting a seat change would be your safest bet, and flight crews are typically happy to accommodate if the flight isn’t fully booked. In times when you can’t move, conventional flu prevention methods still apply. Most important of all is to keep your hands clean. Avoid touching your face and use a hand sanitizer often, especially after you touch surfaces that might be coughed or sneezed on; one way that viruses are transmitted is through “droplets” that are released when someone sneezes or coughs. Tray tables, seatbacks, armrests, and control panels for video and audio systems are often covered in germs. Bring a few individually wrapped alcohol wipes, which are just a few dollars for a 50- to 100-count box.

Do Masks Help? Yes and No
Masks are commonly recommended, because wearing one yourself is a factor that you can unconditionally control, but judging the effectiveness of a mask can be complicated. While studies show that surgical masks do help to prevent contagion, alongside frequent hand washing or sanitizing, they really are more effective in not spreading your germs if you’re the one who’s sick.

It gets even trickier when you consider the fact that viruses can also be spread via airborne particles. Theoretically, N95 respirator masks should filter 95 percent of these particles if they're fitted correctly, but that seems like a pretty big if. That’s not to say that every little bit won’t still help; just know that wearing a mask isn’t foolproof -- and perhaps watch this 3M training video on fitting masks properly if you’re truly concerned.

Good to know: After serious outbreaks in the last decade or two, many airlines like JetBlue and Virgin America have confirmed that they carry a small stock of masks on all flights in their medical or service kits.

Other Unexpected Strategies
It’s always a good idea, on or off an airplane, to turn your face away when someone nearby coughs or sneezes. But what else can you do? Start by putting your individual air vent to good use to deflect airborne germs. Just direct the stream between you and your ill neighbor (bring extra layers if you tend to get cold).

You've probably heard the recommendation of drinking lots of water -- doing so helps the bacteria-fighting enzymes in the mucus of your nose, mouth, and eyes stay hydrated and do their jobs. But even better? Swish some salt water, too. Studies indicate that salt water, a natural antiseptic, can fight bacteria or viruses that get stuck in the mucus membranes in the back of the throat.

Throughout the flight, don't forget to keep warm. Cold feet, for example, signal the brain to conserve energy, resulting in decreased blood flow to areas that lose heat quickly. This in turn leaves those areas, including the mucus membranes of your sinuses, with fewer white blood cells to fight off viruses.

Other precautions can start before you even board, like taking zinc tablets to boost your immune system, getting a flu shot, or taking probiotics. Sipping black tea may help, too. Studies suggest that people who sip 20 ounces of black tea daily produce three times more interferons -- powerful proteins that destroy viral invaders on contact -- than those who don’t.