U.S. World Health Organization Assistant Director Keiji Fukuda attends a conference on swine flu in Cancun, Mexico, Friday, July 3, 2009. The World Health Organization's top flu scientist often describes the virus he's studied for years as 'humbling.' And Dr. Keiji Fukuda isn't alone in marvelling at the mercurial nature of influenza. Flu scientists repeat almost as a mantra that the only thing predictable about flu is its unpredictability.
THE CANADIAN PRESS/AP-Miguel Tovar