Variola

Smallpox (Variola major and Variola minor) began to spread in Mesoamerica immediately after the arrival of Europeans.

Edward Jenner had also discovered vaccination using cowpox ( Vaccinia ) to give cross-immunity to smallpox in 1796, and by Pasteur's time this had generally replaced the use of actual smallpox ( Variola ) material in inoculation.

Inoculation, a practice probably as old as the disease itself, is the injection of the variola virus taken from a pustule or scab of a smallpox sufferer into the superficial layers of the skin, commonly on the upper arm of the subject.