Barry's new book is The Great Influenza: The Epic Story of the Deadliest Plague in History. In 1918, the influenza virus emerged, and in the next year killed millions of people. He writes "before that worldwide pandemic faded away in 1920, it would kill more people than any other outbreak of disease in human history." Scientists are still trying to figure out why the virus spread so rapidly and killed so efficiently. The story has relevance today as scientists believe we are due for another flu pandemic.