The Flu is an infection of the respiratory system caused by the influenza virus. There are three types of influenza virus: A, B, and C.

Types A and B are the most severe. The viruses change constantly and different strains circulate around the world every year. The body’s natural defenses cannot keep up with these changes. Therefore, a person should get a flu shot each year.

Type C causes either a very mild illness, or has no symptoms at all. It does not cause epidemics and does not have the severe public health impact that influenza types A and B do.