I err on the other side of caution. I choose to not vaccinate or feed medicated feed. Coccidiosis is every where, and the vaccine may or may not have the particular strain that is in your soil... kind of like getting vaccinated for the common cold. Regarding the Amprolium, again, I choose the flip side of the coin. Amprolium is a thiamin blocker... so it blocks the uptake in the pathogen as well as the chick, which can lead to some nutritional issues. So, my approach to the disease risk is to: give them a good dose of pro-biotics (you can buy packets of pro-biotics to mix in the chicks water, or you can give them fermented feed) as soon as they start on feed and water, then follow up with early exposure to my soil by giving them sod chunks to play with. A lot of flock keepers actually give the new chicks some feces contaminated soil from their chicken runs. In the natural world, Mama would be taking the chicks out as soon as they leave the nest, and... from a human perspective it sounds gross, but is quite natural in the animal kingdom... The chicks would be snacking on her poo to build their immunity. (The chicks would be inoculating their gut with the hen's digestive flora as well as any coccidiosis present)
There is no right or wrong decision here. It is certainly not a subject worth arguing about, but i did want to take a moment to present the other side of the medication issue.