How Smallpox Spread
By Essence Davison
If a person catches small pox (Variola Virus) and lives, they develop immunity to the disease and can never catch it again.
Like other crowd diseases, smallpox spreads from urban centers outwards into non-immune populations until it eventually reaches areas where the population is too thin to allow it to spread any further. Once smallpox runs out of new host bodies, it dies out.
The survivors of smallpox became immune to the disease was common knowledge. As a result, physicians and others intentionally infected healthy persons with smallpox organisms in the hope that the resulting infection would be less severe than the naturally occurring illness and would create immunity. Children were exposed to organisms from persons with mild cases of smallpox, and various forms of materials from persons with smallpox were administered to healthy adults in different ways.