"Drink fresh ginger tea Ginger is a potent anti-viral substance that prevents the adhesion of viruses to the upper respiratory mucosa. If you drink the concoction I recommend below at the first signs of sickness, you can often fight it off successfully. But—and this is a big “but”—you have to drink it at or near the strength I suggest, or it won’t be effective. Some people find this difficult to do, because ginger is so intense, but if you can handle it your immune system will thank you."
From – 7 Tips for Preventing (and Shortening) Colds and Flus