Ferrets require Fervac-D for canine distemper. This shot is required at least twice, three weeks apart, for a young ferret or a ferret with unknown vaccination history, then once a year every year afterwards for the life of the ferret. Canine distemper is extremely contagious. Keeping your ferret indoors is no protection against this deadly disease. If you so much as come into contact with an infected animal, or even where one has been, you can take it home on your clothing to your ferret.
Vaccination is the only protection, there is no cure.
Ferrets also require Imrab-3 for rabies. Ferrets are unlikely to come into contact with rabies, and even if they do, have only slim chance of shedding it in their saliva. There has never been a case in the history of the United States of ferret passing rabies onto a human. However, if your ferret is not vaccinated, and he bites or nips someone, he can and will be killed and tested. A vaccinated ferret will most likely just be quarantined for several days or weeks.