I'd like to preface this post by stating that although I work in an old school veterinary office, I'm a believer in Alternate Therapies for pets as well as people.
The vet offices and the internet are full of tons of different opinions on the effectiveness of vaccines, what should be given and how often. It's confusing to sift through all the information, from vaccinating practically every five minutes to not vaccinating at all.
I hear arguments constantly that the pet doesn't go anywhere, so there is no exposure. WRONG. I'm sure those who believe this don't wash their hands after taking a pee.
Do you buy pet food? Of course. Are you sure that everyone that walked in that store before you thoroughly washed their hands and sanitized the soles of their shoes before coming in the store? Everything you touch, every step you take in that store means you may pick up a virus that you will carry home with you. Especially those big box pet friendly stores with the vet's office in the back. All of those pets, sick and well, are traveling that same path.
So think of the trip to buy pet food as visiting a huge public bathroom of sorts. You're going to take home something besides pet food.
It is physically impossible to prevent all exposure to any virus, be it direct or air born. This is the basis of all vaccines: exposure to a small amount of the virus so the healthy immune system can develop antibodies.
What pets should not be vaccinated? The very young and nursing, pets with an immune system disorder, pets with cancer or other diseases where vaccination would be detrimental.
What vaccinations should your pet get? Rabies is a no brainer, since it's a requirement in most states to license your dogs. I think cats should have rabies vaccines as well, especially the outdoor kitties, as their exposure to wild animals is much higher. Feline Rhinotracheitis, Calcivirus and Panleukopenia (the FVRCP vaccine) are highly contagious, potentially deadly diseases and the rate of prevention with vaccination is high.
In dogs, Distemper and Parvovirus are horrible potentially fatal diseases that should be prevented. I've taken care of enough dogs with these diseases not to wish them on anyone.
These are the core. There are other vaccines that are recommended that you may want to consider depending on your geographic location and risk of exposure.
And, as always, keeping your pet as healthy as it can be goes a long way in disease prevention. No matter what methods of disease prevention you believe in, it's important to do SOMETHING to protect your pet.