Twice yearly, World Health Organization health officials meet to strategize against influenza, a malady that kills at least 250,000 people each year. In a chess match of sorts, they work to predict their opponent's next move, in this case by modifying vaccines to compensate for changes in the critical viral antigen hemagglutinin, which triggers the host's long-term immune memory. It takes several months to manufacture and distribute flu vaccines in sufficient quantities to inoculate vulnerable individuals before an epidemic occurs, making it necessary to anticipate critical antigenic changes well in advance. Until now, this prediction has been a qualitative rather than a quantitative process, performed by WHO's influ-enza committee in February and September.

These predictions have become much more accurate since molecular data for amino acid sequences of the influenza A and B viruses became available in the mid-1980s, but the vaccines still fail to confer adequate protection in a...

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