Quote: For what? Mareks? Coccidiosis? Newcastle/infection Bronchitis? There are MANY vaccinations, and the only thing chick starter has in it is something to help build immunity to the oocysts in the soil that cause a coccidiosis infection.
Medication in feed is to build immunity to coccidiosis, not all sort of other diseases. Most folks do not have their chicks vaccinated for cocci and many never feed medicated feed, either.
There is a misconception that "vaccination" means they are vaccinated for stuff they are not and misconception that medicated feed has anything to do with preventing disease. It really doesn't.
Medicated feed does not prevent disease. It doesn't even prevent cocci if your soil is rampant with it.
If you want to add birds, you do have to quarantine the new ones for at least 4-6 weeks away from the others, so any disease symptoms can come to the surface, especially symptoms of contagious respiratory illness. That is so, if it happens, you do not add them to your flock (yes, you would euthanize them)