Efficacy of a commercial inactivated H5 influenza vaccine against highly pathogenic avian influenza H5N1 in waterfowl evaluated under field conditions.

Highly pathogenic avian influenza virus (HPAIV) can cause devastating losses in the poultry industry. In addition, several HPAIV exhibit a zooanthroponotic potential and can cause fatal infections in humans. These attributes particularly apply to HPAIV H5N1 of Asian origin. Due to the absence of overt clinical symptoms, introduction and subsequent spread of HPAIV H5N1 in domestic waterfowl (especially ducks) may occur undetected, which increases the risk of transspecies transmissions to highly vulnerable gallinaceous poultry and mammals, including humans. Humans may also become infected with HPAIV H5N1 by food products from slaughtered, silently infected ducks. Vaccination against HPAIV can raise a protective barrier against an incursion of HPAIV since, at least under experimental conditions, the reproduction factor R0 lowered to <1, which ensures eradication of the virus. The objective of this study was to analyse whether these results can also be obtained under free-ranging field conditions in commercially reared flocks of goose parents and fattening ducks injected with a licensed, adjuvanted inactivated H5N2 vaccine. The time and labour required for the vaccination of these geese and duck flocks exceeded expected values, mainly due to animal sorting according to foot ring labels. No adverse effects directly associated with vaccination were observed. Serologically, a homogenous H5-specific antibody response was induced. Titres varied with temporal distance from the last application of vaccine. Geese parents were clinically protected against challenge with HPAIV A/Cygnus cygnus/Germany/R65/06 (H5N1), but still could be infected and spread HPAIV H5N1, albeit at lower levels and for shorter periods compared to unvaccinated controls. Fattening Pekin ducks proved to be clinically resistant against challenge virus infection and shed very little virus.