Season 4 Episode 2 | 54m 53s
In 1918, a flu pandemic ripped through the global population with such speed and virulence that by the end of the following year an estimated 40 million people would be dead. Where did this particular flu strain come from, and what made it so deadly? 85 years later, virologists and epidemiologists the world over are still hunting down the answers to those two critical questions.
Problems Playing Video? | Closed Captioning