Question

It is known fact that the milkmaids who had cowpox did not catch smallpox even during the epidermis why is it so

Answer 1

Smallpox vaccine, the first successful vaccine to be developed, was introduced by Edward Jenner in 1796. He followed up his observation that milkmaids who hadpreviously caught cowpox did not later catch smallpox by showing that inoculated cowpoxprotected against inoculated smallpox.
On May 14, 1796, Jenner took fluid from a cowpox blister and scratched it into the skin of James Phipps, an eight-year-old boy. A single blister rose up on the spot, but James soon recovered. On July 1, Jenner inoculated the boy again, this time with smallpox matter, and no disease developed. The vaccine was a success