Short answers, pulled from the story.
Edward Jenner performed the first smallpox vaccine experiment on James Phipps on the 14th of May 1796. This single experiment marked the birth of vaccination and proved that immunity could be engineered rather than risked through infection.
Variolation carried a mortality rate of 0.5 to 2 percent before Edward Jenner developed the smallpox vaccine. This dangerous practice involved deliberately infecting people with actual smallpox scabs to induce immunity.
The British Government Vaccine Establishment began issuing glycerinated calf lymph in 1896 to replace human-to-human transfer. This change aimed to reduce the risk of transmitting other deadly diseases like syphilis, tuberculosis, and tetanus through the vaccine.
Smallpox was officially declared eradicated in 1980 after the last endemic case was recorded in Somalia in 1977. This achievement made smallpox the only human disease to be completely wiped from the face of the earth.
The United States ordered over 200 million doses of ACAM2000, a second-generation vaccine, between 1999 and 2001. This stockpile was built to guard against the possibility of bioterrorism following the September 11 attacks in 2001.
Modern science suggests that the horsepox virus is the closest relative to the vaccinia strains used in modern smallpox vaccines. Whole-genome sequencing in the 1990s and 2000s revealed that some 19th-century vaccines were 99.7% similar to horsepox.