An inactivated H5N1 avian influenza (AI) vaccine (Re-6) that bears the HA and NA genes from a clade 188.8.131.52 H5N1 virus, A/duck/Guangdong/S1322/10 (DK/GD/S1322/10), has been used in domestic poultry in China and other Southeast Asian countries to control clade 184.108.40.206 H5N1viruses since 2012. The efficacy of this vaccine against H5N1 viruses isolated in recent years has not been reported. In this study, we evaluated the protection efficacy of the Re-6 vaccine in chickens against challenge with four clade 220.127.116.11 H5N1 viruses, one clade 18.104.22.168 H5N1 virus, and one clade 7.2 H5N1 virus; these viruses were isolated in mainland China, Hong Kong, and the Democratic People's Republic of Korea between 2011 and 2015. The vaccinated chickens were completely protected (no disease signs, virus shedding, or death) from the challenge with the four clade 22.214.171.124 H5N1 viruses. In the clade 7.2 virus–challenged group, all of the vaccinated chickens remained healthy and survived for the entire 2-wk observation period; virus shedding was only detected from 1 of 10 chickens on day 3 postchallenge. In the clade 126.96.36.199 virus–challenged group, 8 of the 10 vaccinated chickens remained healthy and survived the 2-wk observation period; however, virus shedding was detected from 8 of 10 chickens on day 5 postchallenge. These results indicate that the Re-6 vaccine provides solid protection against clade 188.8.131.52, good protection against clade 7.2, and poor protection against clade 184.108.40.206.
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Vol. 60 • No. 1s