The Great Influenza pandemic killed as many as 100 million worldwide when the global population was less than a third of what it is today. It killed more people in twenty-four weeks than AIDS has killed in twenty-four years, more people in a year than the Black Death of the Middle Ages in a century. It didn't single out the very young and the very old. Half those who died were young people in the prime of life - in their 20's and 30's. By a bizarre and unprecedented stroke it turned the immune system itself into a killer. Two-thirds...