Silent spread of H5N1 in vaccinated poultry

Abstract

International debate on the merits of vaccinating poultry against the H5N1 influenza A virus^1,2,3 has raised concerns about the possibility of an increased risk of between-flock transmission before outbreaks are detected⁴. Here we show that this 'silent spread' can occur because of incomplete protection at the flock level, even if a vaccine is effective in individual birds. The use of unvaccinated sentinels can mitigate, although not completely eliminate, the problem.