Before Edward Jenner discovered and popularized vaccination, the technique of inoculation had long been in use around the world, with more or less success to combat small pox. Doctors had known for centuries that a small and controlled exposure to the deadly virus variola could lead to immunity even if the mechanism was unknown. What doctors and scientists did not know was that there were many strains of the variola virus, some much more deadly than others. Inoculation worked by introducing controlled amounts of the virus into the system and allowing the body to develop natural antibodies to the virus. Edward Jenner was finally able to show that the different variations of variola virus were similar enough that inoculating with a non-lethal version, in this case cowpox, was enough to grant immunity to the lethal forms.
The word inoculation came from the Latin word inoculatus, the past participle of inoculare meaning to graft in, implant, in the horticultural sense of buds on a tree or plant. Inoculate combined the prefix in- and the Latin word oculus which could mean bud or sprout but originally meant eye. It took its modern meaning of implant germs to produce immunity from around the time Lady Montagu brought inoculation back from India around 1714, where she was stationed with her husband, the ambassador Edward Wortley Montagu. Since the advent of vaccines, the word inoculation has been used synonymously with vaccination.
Image of smallpox vaccination site courtesy Centers for Disease Control.