Enjoy my educational content? Well, why not check out my new channel Megaprojects: h→→Subscribe for new videos every day! https://www.youtube.com/user/TodayIFoundOut?sub_confirmation=1 Follow Simon on social media: https://twitter.com/SimonWhistler https://www.instagram.com/simonwhistler/ Never run out of things to say at the water cooler with TodayIFoundOut! Brand new videos 7 days a week! More from TodayIFoundOut: How Did They Get the CGI in the 1993 Jurassic Park to Look So Good? https://youtu.be/l4UuQxjFpfU What Function Does Natural Aspirin Serve in Plants? https://youtu.be/ejLFtO1ieRM In this video: For many millennia, smallpox was one of the most easily transmitted and deadly diseases in the world for humans. In the 20th century alone, when a successful vaccine was already being widely administered in many countries, it is estimated that smallpox still caused somewhere between 300 and 500 million deaths worldwide- Yes million.