Scientists Discover the Cause of the Deadly Spanish Flu

In 1918 the Spanish Flu killed at least 50 million people around the world and was the second deadliest plague in history–after, well, the plague in the 1300s. But how exactly did a flu virus cause such massive death and destruction across the world?

After the Spanish Flu descended on New York City in 1918, its citizens did everything they could to flatten the curve.

Get the full story behind the aches, pains and dangerous history of the flu.

Marcelino Serna came to the U.S. as a undocumented immigrant, and within just a few years, became one of the country's bravest heroes.