Who developed the smallpox vaccine by testing cowpox on the gardener's son?

• A. Edward Jenner
• B. Louis Pasteur
• C. Alexander Fleming
• D. Marie Curie

Answer: (A)

The idea being tested is how the first vaccine came to be: using a harmless related infection to protect against a dangerous disease. Edward Jenner observed that milkmaids who contract cowpox seemed immune to smallpox. He tested this by inoculating a young boy—the gardener’s son—with material from cowpox lesions. After he recovered, the boy was exposed to smallpox and did not develop the disease, demonstrating immunity. This showed that a milder, related infection could train the immune system to block a more dangerous one, laying the foundation for vaccination and giving us the term vaccination from vacca, meaning cow.

Other names listed are known for different breakthroughs: Pasteur advanced vaccine science and germ theory but not this experiment; Fleming discovered penicillin; Curie studied radioactivity.