In the summer of 1580, the first unmistakable influenza pandemic, or worldwide outbreak, arose in Asia. It spread to Africa and then northward, infecting the whole of Europe over a period of six months. Sea explorers and early colonists then spread the influenza plague to the Americas.
Today, annual influenza outbreaks occur in fall and winter, with serious illness and death largely restricted to the very young, very old and the medically fragile. By contrast, global pandemics settle into a pattern of appearing every 10 to 50 years, often striking younger and previously healthy persons with sometimes fatal results.