Tetanus!

The odds that you will contract the Tetanus Disease in a given year are approximately 1 in 7,302,000 (0.000037%)

So, remember that shot you were supposed to get in junior high that made your arm hurt for two days? That prevents Tetanus which is a disease you catch from stepping on rusty nails. It causes your muscles to freeze up which leads to lockjaw which makes you look like a dick permanently. Luckily, we've largely killed off this problem but there are still some rogue rusty nails that the government is tracking down and trying to kill. Until their resistance movement is broken, remember to get another shot every 10 years or so. And be afraid, but not that afraid cause it's pretty rare.

(http://www.bookofodds.com/Health-Illness/Infectious-Disease/Articles/A0448-The-Relative-Rarity-of-Tetanus)