I think I understand how you feel. I'm afraid the bottom line is, there is no vaccine from the biggies, the respiratory diseases and such. That's why you hear quarantine stressed on here. And even it is not perfect; a new flock can be a carrier and have no symptoms for months, but still infect the old flock. Just living on soil is like a cocci vaccine, as near as I can tell; they get exposed over time in small amounts and develop at least some natural immunity; all the amprolium does is keep the cocci numbers in check so they don't get overwhelmed while this is happening.