The flu is a seriously disrupting illness that affects both the body and mind. Symptoms can range from mild to severe, and can last for several days. In some cases, the flu can lead to pneumonia, which can be fatal in rare cases. This season's vaccine is especially effective against the H3N2 strain of the virus, which has caused most of this year's outbreaks. While it is important to get vaccinated against the flu, it's also important to know who are the most common victims of influenza season.