The Origin Of The Vaccine

The inventor of the smallpox vaccine is Edward Jenner. Furthermore, before it got eradicated, about a third of the infected had died.

Before the vaccine, people had found out that by personally exposing to people infected with smallpox you would get a milder form of the disease. 

Edward Jenner had thought that if someone has cowpox, he or she wouldn't get smallpox. Therefore, he had tested it on an eight year old, James. A few months subsequent he put James in  direct contact with a person with smallpox and fortunately found out that he didn't get infected.