In this article in the Annals …. echinacea was found to be no better than placebo. The study was picked up by the NY Times … and many other papers .. and it's now "common knowledge" (according to my wife) that echinacea doesn't help with the common cold.
Not so simple. As the authors point out, they used pure echniacea rather than extract (as many previous studies .. reporting positive results had used) .. and this study used young health subjects rather than middle-aged subjects who may benefit more from a "boost" to the immune system such as echinacea has been demonstrated to provide.