The use of vaccination to combat multiple introductions of Notifiable Avian Influenza viruses of the H5 and H7 subtypes between 2000 and 2006 in Italy

Abstract

Since 1999, Italy has been challenged by several epidemics of Notifiable Avian Influenza (NAI) of the H5 and H7 subtypes, occurring in the densely populated poultry areas of northern part of the country. Vaccination with a conventional vaccine containing a seed strain with a different neuraminidase subtype to the field virus was used to complement biosecurity and restriction measures as part of an overall eradication strategy. This vaccination technique, known as the "DIVA-Differentiating Infected from Vaccinated Animals" system, enabled, the identification of field exposed flocks and ultimately the eradication of H7N1, H7N3 and H5N2 infections. A bivalent H5/H7 prophylactic vaccination programme of defined poultry populations was introduced subsequently to increase their resistance to field infection. Retrospective analysis of the outbreaks identified important reservoir species such as quail, and demonstrated clearly the higher susceptibility of turkeys to infection. Data generated during 6 years of experience with vaccination against Avian Influenza (AI) indicate that it is a useful tool to limit secondary spread and possibly prevent the introduction of AI viruses in a susceptible population. The Italian AI control programme including vaccination was managed in a flexible manner and enabled the continuation of international trade. It is imperative that if vaccination is to be used to combat the current H5N1 epidemic it is used in conjunction with other measures and under official supervision. An extraordinary effort is required from international organisations to accredit control strategies so that harmonised and validated programs can be implemented. Transparency and sharing of field results from countries that are practising such programmes is crucial to the progressive control and ultimately the eradication of NAI infections in the animal reservoir.