You might try following the link in
@Stravager 's post above, post #4. It should answer most of your questions about medicated feed and Coccidiosis. I'll try to give a few highlights but it can get confusing with all the "if's.
You need to check what medicine is in medicated feed. Usually in the USA it is Amprolium but there are a few that have something else.
Feeding them medicated feed does no good unless they have been exposed to the protozoa that causes Coccidiosis.
Vaccinated chicks cannot pass a virus on to other chickens. The vaccine is made from a form of Marek's virus that affect only turkeys, not chickens. The vaccine does not stop them catching Marek's, it stops the tumors that cause the problems from forming.
Parents cannot pass protection they get from vaccination to their chicks, either through the eggs or in person. It just doesn't work that way.
I just saw your post where you did follow that link. You can feed that medicated feed to not vaccinated chicks if you wish. It will not hurt them. I'd only feed the medicated feed to them and not mix it with any other feed until it is gone. Otherwise you can water down the dosage of the Amprolium to where it doesn't help you if you need the help. But remember, if you feed medicated feed to vaccinated chicks you can negate the vaccination.
They will still get the immunity if you feed them dirt from the run if you already have that protozoa in your flock. If you don't have it present they will not get any immunity from the medicated feed.