Most avian influenza (AI) vaccination and field studies have focused on chickens and turkeys because of their high death rates and the large amounts of highly pathogenic avian influenza (HPAI) virus that they excrete into the environment when infected. Data on vaccination of other species against HPAI remain limited. An increasing number of studies have been conducted to test the efficacy of inactivated vaccines in ducks and geese since it became clear that these species are a source of HPAI H5N1. One problem is the varying susceptibility of waterfowl to H5N1 in general, and to different H5N1 clades in particular. This makes the extrapolation of protection results obtained for a particular waterfowl species against a particular viral strain very difficult. At present, the vaccine industry only produces and licenses products for chickens and turkeys. Since the market for other birds is small, it does not invest heavily in testing products in other species. Most information on vaccination in other birds comes from zoo vaccination, and consists solely of serological data. Whenever experimental challenge was performed in birds other than chickens and turkeys, vaccination using inactivated vaccines always protected against disease and mortality, provided the vaccine was sufficiently matched antigenically with the challenge virus. Inactivated vaccines induce good antibody titres in most species when applied twice and when body weight is taken into account. Until the advent of more specific waterfowl vaccines that can be used in day-old chicks, inactivated vaccines can be applied to protect not only chickens and turkeys but also ducks and other valuable and/or endangered bird species.
