Fortunately, there are simple steps just about anyone can take to avoid the flu.
Colds and flu are both caused by viruses, which are infectious microorganisms that invade your body and can make you sick. You catch these bugs by inhaling water droplets in the air from the breath of an infected person, who spews them out every time he or she exhales, coughs, or sneezes. Cold and flu viruses can roost on inanimate objects too. Twist a contaminated doorknob or use a coworker's pencil before touching your lips, and you can become infected.
The best daily defense against catching a flu virus is as easy as turning on a faucet. After using the restroom, always wash your hands with warm soapy water. Wet your hands before applying soap and rub them together for 20 seconds or so. Shut the water off with a paper towel or your elbow to avoid recontamination. If possible, use an air dryer to dry your hands.
And then there's the flu vaccine. A flu vaccine puts your immune system on alert. It's like giving your antibodies -- the immune system's foot soldiers in the war against germs -- a photo of the enemy, so they'll recognize a flu virus immediately if one invades. In fact, if you've already been infected with a flu virus, your immune system "remembers" what it looks like and attacks the bug before it can make you sick if it reenters your body.
The flu vaccine isn't perfect. Since there are so many strains of influenza raging around the world at any given time, it would be impossible to concoct a supervaccine that would protect against all of them. So the World Health Organization (WHO) gathers information from international public health agencies and determines which three strains are most likely to cause widespread illnesses in the coming flu season. Using that information, drug companies prepare a new vaccine every year that is specially designed to combat those three flu strains.