I don't know about Koi herpes virus but if it is similar to HSV 1 or 2 there are no human vaccines yet on the market as far as I know, but I would look at the papers on live herpes vaccines. One was produced by Cantab (called DISC) which was extremely effective preclinically. Another has been produced by Biovex which were since bought by Amgen. This I think is planned to be used as a therapeutic cancer vaccine, but was also very effective in vitro against HSV-2 preclinically.
I agree in human herpesviruses only varicella zoster vaccine prove to be effective to prevent chickenpox. But it is not really clear how it is working.