Smallpox is 10,000+ years old was responsible for an estimated 300–500 million deaths during the 20th century alone. It killed between 20–60 percent of those infected and and over 80 percent of infected children. It caused lifetime issues for ~85% of the survivors including ~1/3 of all historical cases of blindness. As recently as 1967, the World Health Organization estimated that 15 million people contracted the disease and that two million died in that year.

Highlights include the epidemic of 735–737 is believed to have killed as much as one-third of the population. At least seven religious deities have been specifically dedicated to smallpox. By the mid-18th century smallpox was a major endemic disease everywhere in the world except in Australia and in several small islands. In Europe smallpox was a leading cause of death in the 18th century, killing an estimated 400,000 Europeans each year, including five kings. Up to 10 percent of Swedish infants died of smallpox each year,[10] and the death rate of infants in Russia may have been even higher.

https://en.wikipedia.org/wiki/Smallpox https://en.wikipedia.org/wiki/History_of_smallpox