In Ontario, all cats and dogs are required to be vaccinated for rabies, even if your cat is an indoor cat. It IS the law and mandatory. Should your cat bite a house guest, or groomer, it must be reported to health officials. Without proof of rabies vaccinations, the cat will be placed in quarantine. This is an ugly situation easily avoided.
It may surprise you that cats have more contagious diseases than dogs and that they are easily spread and can be fatal. Cats are especially good at hiding illness. They are very susceptible to airborne respiratory viruses, diseases that are transmitted by cat bites and scratches, and other contagious viruses transmitted through body fluids. So unless you own one single cat its entire life, and it never leaves the house, nor do other cats come in, you are putting your cat at serious risk without vaccinations.
Having said that, I should point out that not every cat needs to be vaccinated for every disease. There are core vaccines, started during kitten-hood, and there are non-core vaccines that are critical in protecting your cat if it has an indoor/outdoor lifestyle.
The core vaccines are against Panleukopenia (feline distemper), Feline Calicivirus, and Feline Rhinotracheitis (Feline Herpes). In short form, this vaccine is called the FVRCP and it is administered every four weeks ideally starting at 7-9 weeks, then 12 weeks, and finally at 16 weeks along with the rabies vaccine. Each cat needs three rounds of the FVRCP to be fully protected.
If you have acquired a re-homed adult cat with no vaccination history, I strongly recommend following the same vaccine protocol no matter what its age and get tested for FeLV as well.
Non-core vaccines your cat may need if it has an indoor/outdoor lifestyle are: Feline Leukemia Virus (FeLV) , Chylamydophile felis, Feline Immunodeficiency Virus (FIV) and Feline Infectious Peritonitis (FIP). These are administered starting at 12 weeks and again at 16 weeks. These diseases are transmitted by bites, body fluids, and are highly contagious. They create chronic immune compromised diseases and infections and it is a terrible, long, drawn out way to suffer. FeLV is the leading cause of illness and death in cats and part of the reason outdoor cats typically have less than half the lifespan of their indoor peers, aside from being killed by cars or poisoning.
Once your cat is fully vaccinated, it is up to you and your vet to determine the lifelong vaccination schedule. Some recommend annually, others do not. My only requirement is that vaccinations have occurred. I do not think any client would be thrilled in knowing there were unvaccinated cats in the same room as their own vaccinated pet, even though surfaces, tools and hands are disinfected between clients.
I believe in maintaining high standards of care for the long-term well-being of every animal and owner who visit my salon. If you object to spending money to protect the health of your cat and others by not vaccinating, than I am not the feline grooming salon for you.