Where are you located—state or country? Most people do not routinely vaccinate chicks unless it is a Mareks vaccine, or occasionly a coccidiosis vaccine when chicks are bought from a hatchery as day-old chicks. In some areas of the world, there may be a need to protect against certain diseases that may be present in the area. Some choose to vaccinate for MG, infectious bronchitis, or Newcastles if they have had experience with these in their flocks before. Fowl pox vaccine might be considered if you live in a tropical area where mosquitoes are bad.
Commercial operations vaccinate for lots of things but that will always be as chicks and because they pack so many birds in a building, any disease will spread like wildfire.
There is no need to vaccinate 6 month old chickens for anything.
I hatch a lot but I've never vaccinated any of my chicks.