I did a bit of a search and really couldn't find much. Most of what I found was just "canned" recommendations that senior cats continue to receive their boosters.
I did find this page, and toward the bottom of it, it speaks to whether one should give boosters to their senior; what situations you shouldn't, etc. It also mentioned that you can have your Vet do bloodwork to run titres (antibody level) on the various things your cat has previously been vaccinated. This makes the most sense to me. If bloodwork reveals the cat is still immune to "whatever", why give them a booster?
I have 5 indoor cats, ranging in ages from about 10 yrs to 16 yrs. I stopped vaccinating them years ago. It was actually a good Vet I had wayyyyyyyy back then who told me that with his own cats, he only vaccinated them (boosters) every 3 years. That got me to thinking and reading. As a result, I decided not to continue vaccinating. They've never come down with anything, not even so much as an upper respiratory infection.....we've been very lucky.
However, my 2nd oldest, Taco, has vaccine associated sarcoma. That's a tough one for me. It says a cat can develop this, up to 13 yrs after their last vaccination (that would be about right for him). This makes me angry. He's a gorgeous cuddly big boy who's underwent 2 lump removal surgeries (Apr and May) but the tumor returned, with a vengence. He now has a large scruff tumor the size of half an egg, and one on his right side near shoulder blade that's about an inch from the scruff tumor. They don't seem to be bothering him at all, he seems very healthy otherwise, maintaining his weight of 18.5 lbs, appetite good............but it makes me angry that something I gave to protect him will be what takes him.
Oops, here's the link to that article:http://cats.about.com/cs/vaccination...cination_2.htm
I guess there's a lot of things to consider when making the decision. Does the cat ever go outside? Ever come into contact with non-vaccinated cats? Does the cat have any chronic health issues? Any problems with the immune system? Any previous reaction to a vaccine/booster?
As far as I'm concerned, boosters are the brain-children of Vets who want to make $$. Why do some tell owners they MUST continue yearly while other Vets say every 3 years? Makes you wonder. I'm an RN and I'm all for children being vaccinated........but lets be real, humans don't continue to receive boosters for the remainder of their lives so why would an animal? Maybe my cats are just lucky but to me, they're living proof that cats can live a healthy life without them. I used to remember how the boosters would make 2 of them so ill for a few days. That's a huge assault to their bodies. Just my 2 CDN cents :-)