Worldwide Flu Outbreaks
A major mutation of a flu strain usually occurs every 10 years and can cause a flu pandemic - a worldwide outbreak. The last time there was a mutation similar to this year's Fujian strain, nearly 65,000 people died - and that was only five years ago. Still, while health officials say the world is overdue for another flu pandemic, there is no sign of that happening this season.
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Sources: Associated Press, Centers For Disease Control and Prevention, World Health Organization, Food and Drug Administration