Keeping the flyes down is a great way to help prevent pinkeye. Remember that you need to use different products every year though. Atleast in california the flyes get imune to products but if we use different dust bag powders, different ear tags etc. That really helps keep the fly population down. We also vaccinate every year. I can say that it works well in our herd and the only other problem we have is getting it after having a foxtail in there eye. Then sometimes we see a little pinkeye start but we can usually get it to go away with a little care. It is our opinion that the vacine is a good investment in our area!