THE RECORD
What changed
In 1796 Jenner tested whether cowpox exposure protected James Phipps from smallpox and published in 1798.
EVIDENCE
What remains
Jenner's case report, images, vaccination records and later statistics document efficacy and spread.
WHY IT MATTERS
Why it matters
It opened population-scale prevention and ultimately contributed to smallpox eradication in 1980.
OPEN QUESTION
Where interpretation begins
Variolation long existed across Asia, Africa, the Ottoman world and Europe; the non-consensual experiment on a child raises ethical problems.