Feeding Medicated chick feed to vaccinated chicks?

[Kiki]

Apparently. He also bought a kennel to put them in. He said he got it next to nothing price wise.

I'd be worried it was old feed. Ask him to get pictures of the date on the feed bag for you.
Feeding old feed is not a good idea. Make sure it's fresh or decline it.

 

[Kiki]

I don’t think I’ve had coccidiosis in the past. We do have older birds but they weren’t ever vaccinated. We had a few die here and there.

I would not feed medicated if I were you.

 

[NatJ]

I don’t think I’ve had coccidiosis in the past. We do have older birds but they weren’t ever vaccinated. We had a few die here and there.

I might offer the medicated chick starter to the older chickens.
Check what medication, but amprolium (common medication in the USA) is safe for laying hens, and you can keep eating the eggs. Amprolium just blocks one vitamin that coccidiosis needs, so the coccidiosis cannot grow but the chickens are fine.

Chick starter is fine for adult chickens, as long as the hens also have access to a calcium source (like oyster shells.) Chick starter has enough of everything else they need.

I purchased some chicks from Hoover Hachery and they were medicated against mereks and cocci...

Cancels out the vaccine? Like the shots wouldn't be effective anymore?

Correct. Chick starter that is medicated to prevent coccidiosis makes that vaccine not effective for those chicks.

It will have no effect on the Mareks vaccine.