So the medication in medicated feed is for an entirely different ailment than anything chickens are vaccinated against.  Two unrelated diseases and unrelated treatments, so don't let the vaccination they supposedly had weigh into your decision whether or not to feed medicated feed, which is to help prevent coccidiosis.  It's really personal choice whether or not to feed medicated feed.  They will be exposed to cocci as soon as they go outdoors (if they haven't been exposed already) and some chicks can handle the load in their systems just fine while others cannot.  It is ok to switch to non-medicated feed for your next bag, just keep an eye out for any signs of coccidiosis and be prepared to treat with corid if necessary.