Why Are Flu Viruses Seasonal?

Heide Benser / Corbis

From Time Magazine:

U.S. health officials are bracing for a resurgence of the new H1N1/09 flu virus this fall, when the influenza season kicks into high gear with the resurgence of cold weather. By October, the government hopes to have 120 million doses of vaccine ready to fight the new virus, which is currently spreading around the world in the first pandemic in more than 40 years. Already, H1N1 is hitting the southern hemisphere hard: Argentina has recorded more than 160 deaths from H1N1, second most after the U.S. That's because it's winter in the southern hemisphere, and flu infections tend to spike during the fall and winter months in temperate countries.

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