I like the Gaia Herbs Quick Defense. If you start feeling under the weather and you pick up on it right away, this is the formula to go with. For me, it’s a tickle in my nose. As long as I take 2 of these guys five times a day, I’m fine and I usually only take it that first day.  It’s a supercritical extract of Echinacea and elderberry and it works wonders.