Millions of Americans get vaccinated for the flu each year. During the 2011-2012 flu season, 132.8 million doses of flu vaccine were distributed in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC). That's a lot of shots, but it doesn't even cover half of the U.S. population. Many opt out of influenza protection because they don't know much about it. Dec. 2-8, 2012 is National Influenza Vaccination Week, a campaign organized by the CDC to encourage vaccination. Test your knowledge of the flu and flu vaccine with this quiz.