Vaccination policy applied for the control of avian influenza in Italy

This paper describes the measures applied to control the re-emergence of the low pathogenicity avian influenza virus of the H7N1 subtype which followed the devastating HPAI epidemic in Italy between 1999 and 2000. To control the LPAI virus and to develop a novel control strategy, a "DIVA" (Differentiating Infected from Vaccinated Animals) strategy was developed and combined to a strict territorial control programme. The "DIVA" strategy was based on the use of an inactivated oil emulsion vaccine containing the same haemagglutinin (H) sub-type as the field virus, but a different neuraminidase (N). The possibility of using the diverse N group, to differentiate between vaccinated and naturally infected birds, was achieved through the development of an "ad hoc" serological test based on the detection of specific anti-N1 antibodies. The control programme included an intensive sero-surveillance programme aiming at detecting the circulation of the LPAI virus, through the regular testing of vaccinated and unvaccinated flocks and the evaluation of the efficacy of the vaccination schemes in the field. The experience gained during the Italian 1999-2001 AI epidemic, suggests that the combination of a "DIVA" control strategy with a territorial monitoring system under official control can represent an effective tool for the control of avian influenza infections in poultry. In addition, the application of a "DIVA" vaccination policy, as opposed to a conventional policy enabled veterinary public health organisations to establish that infection was not circulating any longer, and ultimately resulted in the possibility of marketing meat obtained from animals vaccinated against an OIE List A disease.