The problem with vaccinating is that it usually comes in packs that are meant for commercial flocks, so a pack will often do a minimum of 500 birds. We decided for the few chickens etc that we hatch it wasn't cost effective to vaccinate and so far we haven't had a problem. I think that good husbandry eg heat, food, water, not over-crowding will go a long way to keeping the chicks/poults healthy.