The Rinko article states: "Please note that this 'IgY Food' doesn't aim at curing KHV virus disease for the koi."
Elsewhere it states: "This is essentially different from the KHV vaccine developed in Israel. Vaccination aims at letting the fish make an antibody in a direct way, while Japan's product is designed as a supplement type of medicine to the diet." ... translation clarity is an issue.
My impression is that the food has to be used continuously. The chicken-produced antibody does battle with the virus, but does not cause the carp to produce antibodies of its own.
[Being almost as cynical as Luke for a moment, the combination of widespread use of the Israeli vaccine and a patent on this chicken-produced antibody would make for a level of financial success few koi breeders can ever hope to attain.]