The dangers of vaccinating against flu if the vaccine is not a perfect match for the disease strain have been highlighted by a horse study.
Andrew Park鈥檚 team at the Animal Health Trust near Newmarket, UK, tested vaccines that were either identical or slightly different to a strain of flu infecting ponies. The ponies given mismatched vaccine were more likely to become infected and to excrete live flu virus, and also stayed infectious longer than ponies with a well-matched vaccine. 鈥淭he longer infectious period allows the virus more replication cycles, and a greater chance to evolve,鈥� says co-author James Wood. And when the researchers put their results into an epidemic model, they found the risk of large outbreaks after using a mismatched vaccine to be up to 1000 times higher than after a well-matched vaccination (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2004.2766).
This kind of flawed vaccination may have allowed flu mutants to evolve in vaccinated poultry in Mexico (New 杏吧原创, 27 March, p 6). The work also raises further concerns about widespread poultry vaccination in China. A virulent new bird flu devastated birds across east Asia this year and also killed 22 people.
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