IMMUNOLOGY

Detailed explanation-1: -The basis for vaccination began in 1796 when the English doctor Edward Jenner noticed that milkmaids who had gotten cowpox were protected from smallpox. Jenner also knew about variolation and guessed that exposure to cowpox could be used to protect against smallpox.

Detailed explanation-2: -He diagnosed cowpox rather than smallpox and Sarah confirmed that one of her cows, a Gloucester cow called Blossom, had recently had cowpox. Edward Jenner realised that this was his opportunity to test the protective properties of cowpox by giving it to someone who had not yet suffered smallpox.

Detailed explanation-3: -cowpox, also called vaccinia, uncommon mildly eruptive disease of animals, first observed in cows and occurring particularly in cats, that when transmitted to otherwise healthy humans produces immunity to smallpox. The cowpox virus is closely related to variola, the causative virus of smallpox.