I know many people who do tetanus vaccines every couple of years and nothing else, but their horses are rarely off-site. I think if you are going to shows and clinics and mixing with a variety of horses on a regular basis, I would really rather be covered. There is a note on my insurance that states that vaccinations must be kept up to date, so anyone who decides not to follow a yearly vaccination schedule should check their policies to make sure that the policy will support it. Some state "regular" vaccinations, rather than "annual" so on that basis and some policies don't mention vaccinations at all so long as the horse is cared for and kept in good health.