I don't think that the coccidiosis vaccine is all that useful, rather using the medicated feed is a better option. It needs to be fed for a couple of weeks AFTER the chicks are exposed to your soil and run, so don't stop feeding it too soon! I'd rather not wait to have sick and dying, or stunted, chicks, so if there's any doubt, the medicated chick starter is a good product to use.
Mary
Mary