The virus then spread to Alaska and Canada. From there it spread to the continental U.S. and western Europe. From Europe, the flu spread to the Southern Hemisphere. Because global travel is now so easy, many scientists fear that the flu will affect 40 percent of the world s population. Pandemics are characterized by antigenic shifts and are associated with severe illness and significant mortality on a global scale.
Epidemics are less severe regional outbreaks that involve fewer people.
At least five pandemics and several major epidemics have been reported over the years, and these are just a few. This flu killed an estimated 40 million individuals, making it the killer of more people than any other single event in world history. The virus infected people from Chile to Alaska and then mysteriously disappeared. Scientists are still trying to figure out exactly where this virus came from and how it was transported around the world. In 1977-78 a strain of virus identical to one that caused an epidemic in 1950 returned, affecting mostly people under the age of 25.