I have what I consider a healthy skepticism about certain traditional Chinese medical practices, but several years ago a friend recommended I try Yu Ping Feng San Wan to help ward off the 2-3 colds I was getting every winter. Astragalus is the main ingredient, but it contains a number of other herbs which potentiate the astragalus. Since then I have had just one cold in the last 3 years (ironically I caught it from my wife who had just returned from China with the bug in January a year ago). I teach at a university and am surrounded by students who in the winter are always happily hacking disease vectors. But this stuff seems to really work. Jade Screen is the most popular brand. You can find distributors by googling. Worth a try if you're prone to multiple colds as I was.

Jon