Cold and flu virus-laden droplets may remain infectious for several hours, depending on where they fall. Viruses generally remain active longer on stainless steel, plastic and similar hard surfaces than on fabric and other soft surfaces. Other factors, such as the amount of virus deposited on a surface and the temperature and humidity of the environment, also determine how long cold and flu viruses stay active outside the body.
It's possible to catch the flu or a cold after handling an object an infected person sneezed or coughed on a few moments ago. But personal contact with an infected person — such as a handshake or breathing in droplets from a cough or sneeze — is the most common way these viruses spread.
The best way to avoid becoming infected with a cold or flu virus is to wash your hands frequently with soap and water or with an alcohol-based sanitizer. Also avoid touching your nose, mouth and eyes or biting your nails. Most importantly — get a flu vaccine every year.