The earliest methods of immunization and protection against smallpox date back to the year 1000 A.D., when the son of a Chinese statesman was said to have been inoculated against smallpox by having powder from pulverized smallpox scabs blown into his nose. When material from an infected individual is introduced as protection for another, it is called variolation. It took six centuries before variolation was introduced to Great Britain in 1721.
Reference: Hussein H, et al. Front Public Health. 2015;3:269.