The Spanish Flu of 1918 killed between 50 and 100 million people. It infected a third of the world’s population. But it’s likely that, if you’re thinking of the most important events of the 20th century, the Spanish Flu probably doesn’t immediately spring to mind. Why is that? To find out, and to explore exactly how it reshaped society, we talked with Laura Spinney, author of the book “Pale Rader: The Spanish Flu of 1918 and How It Changed the World.”