Unfortunately, the available research discounts this as being effective. More likely you will still catch the illnesses but recover more quickly from them when you do. One interesting point about the research done on Echinacea. Many of the human studies used an injectable form of the herb and not the oral form we buy at the store. Anyone allergic to ragweed, daisies, sunflowers or marigolds might also be allergic to Echinacea.
Experts recommend taking it for no longer than eight weeks at a time.
Again the research supporting its use for the prevention of upper respiratory infections is much weaker than that for the treatment of the infection once it starts. Used under License.