For the longest time, smallpox was one of the biggest killers of human beings. The virus causes painful lesions and blisters throughout a person’s body, high fevers, and killed around 30 percent of all people who were infected with it.
We are now lucky enough to live in a world without smallpox, but the death tolls were still remarkably high in the 20th century. Last century alone saw a total of 300 million people. Had a smallpox vaccine not been invented, it would continue to kill us today.