If you feed medicated chick feed and vaccinate your chicks for Coccidiosis as well, the two treatments will cancel each other out and you will end up with your young chicks dying from Coccidiosis.
For the umpteenth 1,000,000th time, Medicated chick food does not contain ANY medicine, ZILCH, NADA, ZERO.
Medicated chick food however does contain a synthetic form of protein that the one celled Coccidiosis parasite is unable to degenerate from real Protein. This analog form of protein is consumed by the Coccidiosis parasite and it dies from slow starvation. But not before the bird builds up a natural immunity to the weakened Coccidiosis parasite. So feeding medicated chick feed and vaccinating too, just cancels each other out. You get the worst of both worlds.
The medicated feed kills off the Coccidiosis parasite BEFORE the vaccine made from a weakened Coccisiosis cell can confer immunity.