http://www.cdc.gov/flu/protect/keyfacts.htm
This document also available in Spanish
Centers for Disease Control and Prevention, U.S. Department of Health and Human Services
The single best way to protect against the flu is to get vaccinated. This fact sheet discusses the two types of flu vaccine, best time to get vaccinated, and who should and should not get vaccinated. The fact sheet also discusses flu vaccine effectiveness and side effects.