Carrie
This is definitely one of those "hot topics" for those who want to provide care as naturally as possible, and have to consider vaccination requirements. The same goes for dogs and cats that may have to be boarded from time to time. For my own horse, I have been lucky to find a barn that does require vaccinations, but after talking with the barn owner and explaining that my horse has chronic lyme, and reactions to vaccines, she talked to her vet, and the vet recommended that I vaccinate for those diseases my horse could spread directly horse to horse. This really only meant Flu/Rhino. EWT, West Nile, Potomac, tetnus are all diseases the horse is exposed to in their environment, and don't necessarily spread directly horse to horse. I've had multiple vets conclude that the strangles vaccine was worthless, and fortunately, this one agreed.
Basically, I'm quite lucky at the moment, only having to vaccinate for flu/rhino. Most general boarding barns do require a lot of vaccinations, but it's the show horses that are constantly moving that really get hit even harder with exposure, and more vaccinations. It's a double whammy as their immune systems are quite often weakened from the constant moving around and stress of being a show horse.