Who began immunology by showing that vaccination with pus from cowpox prevented smallpox?

• A. Edward Jenner
• B. Louis Pasteur
• C. Alexander Fleming
• D. Ignaz Semmelweis

Answer: (A)

Vaccination to prevent disease originated with Edward Jenner, who showed that material from cowpox could protect against smallpox. He observed that milkmaids who contracted cowpox rarely got smallpox, then tested the idea by inoculating a boy with cowpox and later exposing him to smallpox; the boy remained protected. This demonstrated that a milder infection could train the immune system to resist a more dangerous one, launching the field of immunology and the vaccine approach. Jenner’s work gave rise to the term vaccination, from vaccinia, the cow-derived agent. Later scientists like Louis Pasteur expanded on vaccines and immune concepts, while Alexander Fleming and Ignaz Semmelweis made important contributions in other areas of microbiology. But the origin of immunology through vaccination is credited to Jenner.