https://en.wikipedia.org/wiki/Smallpox
The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) certified the global eradication of the disease in 1980, making it the only human disease to be eradicated.
The risk of death was about 30%, with higher rates among babies.
In 18th-century Europe, it is estimated that 400,000 people died from the disease per year, and that one-third of all cases of blindness were due to smallpox. Smallpox is estimated to have killed up to 300 million people in the 20th century and around 500 million people in the last 100 years of its existence.
The first clear reference to smallpox inoculation was made by the Chinese author Wan Quan (1499–1582) in his Dòuzhěn xīnfǎ (痘疹心法) published in 1549, with earliest hints of the practice in China during the 10th century. In China, powdered smallpox scabs were blown up the noses of the healthy. People would then develop a mild case of the disease and from then on were immune to it. The technique did have a 0.5–2.0% mortality rate, but that was considerably less than the 20–30% mortality rate of the disease itself.
The English physician Edward Jenner demonstrated the effectiveness of cowpox to protect humans from smallpox in 1796… In Jenner’s time, smallpox killed around 10% of the population, with the number as high as 20% in towns and cities where infection spread more easily
In the Easter Islands
1870-80 only 100 people left… ~97% of the population dead or gone in less than a decade (ostensibly due to disease), much of the island’s cultural knowledge had been lost.