Jenner · Vaccination
Can a mild illness protect you from a deadly one?
That time, that place
A country doctor. Smallpox was killing hundreds of thousands a year in Europe, and those who survived kept deep scars.
A preventive of sorts existed: take matter from a patient's pustule and introduce it into a healthy person. But that was still smallpox. Many came through it lightly; some died.
Why this question
The countryside carried an old saying: milkmaids do not get smallpox.
They had one thing in common. They had all had cowpox — blisters on the hands, a few days of mild illness, and it passed.
What was found
Jenner took matter from a cowpox blister on a milkmaid's hand and introduced it into an eight-year-old boy. The boy fell mildly ill and recovered.
Six weeks later he inoculated the same boy with actual smallpox. Nothing happened.
He repeated the sequence with others, confirmed it, and published. Why it worked he did not know. There was as yet no concept of immunity.
To be spared smallpox you had to survive smallpox
Cases that resisted smallpox after having had cowpox
The word vaccine comes from the Latin for cow. In 1980 smallpox became the only human disease humanity has erased from the Earth