Every year, usually between December and May, between 5% and 20% of the population in the U.S. become ill with the flu, or influenza. This is the normal course of seasonal flu with which we have become accustomed. It can cause serious illness and even death in the very young, the elderly and other individuals with impaired resistance and chronic illness. For this reason, everyone should get a flu shot unless your health care provider advises you otherwise.
In 1918, 1957 and 1968, the flu season in the U.S. was especially severe and resulted in a much higher number of illnesses and deaths. This more dangerous form is calledpandemic flu. Public health experts believe that a flu pandemic is likely to occur again in the future and worry that a mutant form of avian flu, under certain circumstances, could eventually cause a flu pandemic.