I didn't do it this time.
He said this year he hasn't treated any cases, nor heard of any local outbreaks... that some years, there's an exposure at a show or a barn and it spreads all over, but not right now.
He also said to be serious about immunity for it, it really needs to be given every six months. He said he wouldn't worry about it in my circumstance where they seldom have contact with other horses, just passing on trail.