As the 18th century was winding to a close, an English physician named Edward Jenner set about to determine whether there was any truth to an urban legend of his day: milkmaids who got cowpox (a disease that causes ulcers on cows' teats and can be spread to humans at the site of a scratch or abrasion) didn't get smallpox. This was a big deal, because a case of cowpox would typically leave a person with a self-contained and localized ulcer or two (usually on a hand) and never killed anyone while a case of smallpox would likely cause disfiguring scars at best and full-on death at worst.
In a process that likely would not get *FDA approval today, Jenner inoculated an eight-year-old boy (one James Phipps) with what taken from a milkmaid's cowpox sores. After the boy contracted and recovered from cowpox, Jenner went on to inoculate him with smallpox. The boy was immune, and did not contract the disease. Jenner repeated this process with 22 more lucky folks.
The terms vaccine and vaccination are derived from Variolae vaccinae (smallpox of the cow), the term devised by him who both developed the concept of vaccines and created the first vaccine to denote cowpox. He used the phrase in 1798 for the long title of his Inquiry into the Variolae vaccinae Known as the Cow Pox, in which he described the protective effect of cowpox against smallpox. In 1881, to honor Jenner, Louis Pasteur proposed that the terms should be extended to cover the new protective inoculations then being developed.
After being inoculated with smallpox, the boy ____________.