Vaccination of chickens against H5N1 avian influenza in the face of an outbreak interrupts virus transmission

Abstract

Vaccination of chickens with a commercially available killed H5N2 vaccine was being evaluated as an additional tool to enhanced biosecurity measures and intensive surveillance for control of highly pathogenic avian influenza subtype H5N1 disease in Hong Kong in 2002. In December 2002 to January 2003, there were outbreaks of H5N1 disease in waterfowl in two recreational parks, wild water birds, several poultry markets and five chicken farms. In addition to quarantine, depopulation of the affected sheds and increased biosecurity, vaccination of the unaffected sheds and surrounding unvaccinated farms was undertaken on three farms. In at least two farms, infection spread to the recently vaccinated sheds with low rates of H5N1 mortality in sheds when the chickens were between 9 and 18 days post-vaccination. However, after 18 days post-vaccination no more deaths from H5N1 avian influenza occurred and intensive monitoring by virus culture on these farms showed no evidence of asymptomatic shedding of the virus. This provides evidence that H5 vaccine can interrupt virus transmission in a field setting.

Antigenic Profile of Avian H5N1 Viruses in Asia from 2002 to 2007

“…Poultry has a relatively short life span, and massive seasonal vaccinations of poultry against avian influenza virus are a recent development (25,33). In unvaccinated aberrant hosts, such as chicken, infection with highly pathogenic H5N1 virus is lethal (13,20,37). Thus, accumulation of mutations on the HA of avian influenza virus may not be caused by continuous antibody selection, as has occurred with human influenza viruses.…”

Puzzling inefficiency of H5N1 influenza vaccines in Egyptian poultry

“…Furthermore, field trials of oil emulsion-whole-virus H5 vaccines have shown promise in controlling H5N1 influenza outbreaks in Vietnam and the People's Republic of China (41)(42)(43). However, mass vaccination has failed to control the continuing H5N1 HPAI outbreaks in Egypt (22).…”

Effect of H7N1 vaccination on highly pathogenic avian influenza H7N7 virus transmission in turkeys

“…Vaccination is considered an important tool in the prevention and control of AI. A field trial with H5N2 vaccine in Hong Kong in 2002 showed that vaccinated chickens were protected from disease, and HPAI H5N1 virus transmission was reduced [2]. The same was concluded for vaccination with H5N1 and H5N2 vaccines in Vietnam (2005) [3] and Mexico (1995) [4], although due to the various control strategies and vaccines implemented during these epidemics it was not possible to claim a direct relationship between reduced transmission and the applied vaccination strategy.…”