Coccidiosis is an infection caused by a protozoan, and it is found in most environments. However, the coccidiosis vaccine administered in the U.S. is unattenuated, meaning it is not weakened in any way, and can actually cause illness and retarded growth. We think it's a bad idea to cause the baby chicks to endure the extra stress of cocci vaccinations, since shipping is already stressful on the babies. It's for that reason we don't offer a vaccination against coccidia.
To offer extra protection against cocci, you can offer a medicated chick starter feed--this usually contains amprol, and helps chicks resist coccidia oocysts while they build up their natural immunity. Alternatively, you can simply pay extra attention to keeping their brooder clean and dry. The oocysts proliferate in wet environments. It's usually easier to keep a brooder clean when it has just a few backyard birds in it than it is in a factory-farm environment where birds are raised in the thousands with no individual attention to their welfare. However, some backyard keepers like the extra insurance medicated feed can offer.