Alright...
So if you search medicated vs non medicated there are a good number of threads on this topic.
Simply:
It is your choice to medicate or not.
Medication is usually just amprolium which is a thiamine analog. The uptate of this "fake" thiamine by the cocci inhibits the cocci from reproducing. It does not kill them or treat birds which get a load of cocci which is too high for their bodies to handle. Medicated feed only PREVENTS cocci outbreaks by inhibiting the growth of the protozoa cocci, which is found in all soils to some degree. It helps birds become immune by keeping levels low so they can make their own resistance to them.
You could eat a bowl of medicated starter for breakfast every morning and it will just go right through you. There isn't enough "medicine" in the starter to cause a thiamine deficiency in chicks or well, living thing that has enough cells to be seen by the naked eye.
Med feed will only nullify the cocci vaccine. If you chose to get mericks vaccine, it will not change that. Mericks is viral, cocci is a protozoa. Two totally different biological systems.