I've taken it in the past when my son tested positive for flu, but before I've shown symptoms. I've yet to come down with it under those circumstances. Of cours

I've taken it in the past when my son tested positive for flu, but before I've shown symptoms. I've yet to come down with it under those circumstances. Of course, its impossible to say for sure whether I'd have gotten the flu otherwise, but anecdotally I believe it was successful prophylaxis.