Success Factors for Avian Influenza Vaccine Use in Poultry and Potential Impact at the Wild Bird–Agricultural Interface

Abstract

Thirty-two epizootics of high pathogenicity avian influenza (HPAI) have been reported in poultry and other birds since 1959. The ongoing H5N1 HPAI epizootic that began in 1996 has also spilled over to infect wild birds. Traditional stamping-out programs in poultry have resulted in eradication of most HPAI epizootics. However, vaccination of poultry was added as a control tool in 1995 and has been used during five epizootics. Over 113 billion doses of AI vaccine have been used in poultry from 2002 to 2010 as oil-emulsified, inactivated whole AIV vaccines (95.5%) and live vectored vaccines (4.5%). Over 99% of the vaccine has been used in the four H5N1 HPAI enzootic countries: China including Hong Kong (91%), Egypt (4.7%), Indonesia (2.3%), and Vietnam (1.4%) where vaccination programs have been nationwide and routine to all poultry. Ten other countries used vaccine in poultry in a focused, risk-based manner but this accounted for less than 1% of the vaccine used. Most vaccine "failures" have resulted from problems in the vaccination process; i.e., failure to adequately administer the vaccine to at-risk poultry resulting in lack of population immunity, while fewer failures have resulted from antigenic drift of field viruses away from the vaccine viruses. It is currently not feasible to vaccinate wild birds against H5N1 HPAI, but naturally occurring infections with H5 low pathogenicity avian influenza viruses may generate cross-protective immunity against H5N1 HPAI. The most feasible method to prevent and control H5N1 HPAI in wild birds is through control of the disease in poultry with use of vaccine to reduce environmental burden of H5N1 HPAIV, and eventual eradication of the virus in domestic poultry, especially in domestic ducks which are raised in enzootic countries on range or in other outdoor systems having contact with wild aquatic and periurban terrestrial birds.

Emergence and Evolution of Avian H5N2 Influenza Viruses in Chickens in Taiwan

“…This further supports the possibility that, while apparently prohibited (21), vaccination with an H5N2 virus (potentially a bi-or trivalent vaccine including H6N1 and/or H9N2 viruses) has occurred and that this insufficiently inactivated or inadequately attenuated live-virus vaccine is the source of the H5N2 viruses found in chickens in Taiwan. Widespread vaccination of poultry is commonly used in several countries to provide protection against avian influenza (50). The quality of the vaccine is critical to the success of such programs, while control measures such as stamping out and localized temporary vaccination upon an outbreak could be an alternative (50,51).…”

“…Widespread vaccination of poultry is commonly used in several countries to provide protection against avian influenza (50). The quality of the vaccine is critical to the success of such programs, while control measures such as stamping out and localized temporary vaccination upon an outbreak could be an alternative (50,51). In the case of H5N2 in Taiwan, the reemergence of a North American vaccine strain virus in Asia after approximately 10 years is a strong indication that a vaccine may be the source of this virus.…”

Impacts of poultry vaccination on viruses of wild bird

“…Movement of AIV between farmed poultry and wild birds has been intensively studied, including transmission of highly pathogenic avian influenza viruses (HPAIV) from poultry into wild birds [21][22][23]. Vaccination of poultry may decrease the environmental burden of H5N1 HPAIV in endemic areas and thus limit transmission to wild birds [22]. However the potential for vaccination to drive antigenic drift of field viruses away from vaccine viruses should also be considered [16 ,17].…”

Live poultry vaccines against highly pathogenic avian influenza viruses

“…The immunization with inactivated virus did not prevent virus shedding in birds after being challenged by HPAIVs [5][6][7][8]. Therefore, the inactivated vaccines successfully protected layers and broiler chickens from disease and prevented the decrease in egg production but did not prevent the spread of the virus.…”