Getting smallpox confers lifetime immunity if you survive. Even before vaccination with cowpox was discovered, several cultures around the world discovered that if previously unexposed people were innoculated on the skin with the liquid from pustules of smallpox victims, it was possible to stimulate an immune response with lower risk than natural exposure to smallpox. Normally smallpox is caught by breathing in aerosolized smallpox virus. When the infection is caught in that manner, the death rate is 30-50%. The death rate from exposure on a scratch on the skin was about 1% and the course of the disease was much milder. On problem with this method of innoculation is that the recipients are infectious to those who have not already received it so they had to be isolated.
In the 1850s as a young man, George Washington traveled to an island in the West Indies to undergo this inoculation process called variolination because it used the variola virus. Later after the British used smallpox against Washington's army, Washington had all his men varionlinated. It wasn't till the 1790s that Jenner experimented with cowpox which was much safer than variolination to protect people against smallpox.
I meant the 1750s.