For many years, I had a constant battle with the flu and would often come down with it 3 or 4 times a year. It was particularly bad back around 200 but that was the last bad struggle I had with it as I tried a zapper that I borrowed from a friend. What I found is that if you use it at the very first symptoms, it will go away 9 times out of 10 or better. The remaining times, it may require that you zap some more.