I agree. Especially with all the hype now with WNV. My neighbor has a small herd of Aztecas. Out on 160acres, bordering the wetlands. Never vaccinates. Horses are as sound as can be. He just now started to bring some hay in to get them ""tame"...other than that, they live off the non-irrigated "pasture", together with 25 cows. They are skinny by the end of winter, catch up quickly once grass comes in, stay fat and shiny well into December, and have no problems with that lifestyle. Makes me wonder how much we overdo everything, seriously.
When I was in Italy, where my mare foundered, I didn't dare doing the flu/tetanus shots, after she got so sick from it, and couldn't find tetanus shots only. They just don't have them. So I ended up not vaccinating them for 6 years. NEVER any problems.
They were a closed group, never in close contact with the travelling horses, and were vaccinated earlier in life. Makes me think that immunity lasts a lot longer than we're made to believe. And that, given a chance, they develop immunity to certain diseases too.
Certainly food for thought.