The process of giving someone a vaccine or small amount of disease to help their body develop immunity and fight off illness.
From Latin 'inoculatus' (grafted in), from 'in-' (in) and 'oculare' (to graft), from 'oculus' (eye). Originally meant grafting plants, later applied to medical practice.
Before vaccines were invented, people practiced 'variolation'—deliberately infecting themselves with smallpox pustules from infected people to survive it—incredibly risky but it worked often enough that it was centuries ahead of germ theory.
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