The History of Vaccination

Few medical ideas have saved more lives than vaccination, yet it began with an observation that seemed almost too simple to matter. In late eighteenth-century England, a country doctor named Edward Jenner noticed that milkmaids who had caught a mild disease called cowpox rarely fell ill with smallpox, a far deadlier illness that killed or scarred enormous numbers of people. Acting on this clue, he deliberately exposed a healthy boy to cowpox and later showed that the child did not develop smallpox even when he was exposed to it. Jenner had discovered that a harmless infection could protect against a dangerous one.

The principle behind his discovery is now well understood. When the body successfully fights off an infection, it "remembers" the invader and can respond much faster and more strongly if the same threat ever returns. A vaccine takes clever advantage of this memory by exposing the body to a weakened, killed, or harmless form of a disease, training the immune system to recognize it without causing serious illness. Over the following two centuries, scientists developed vaccines against many diseases that had once killed or disabled enormous numbers of people every year.

Vaccination has not always been welcomed, however. From the very beginning, some people distrusted it, fearing unknown side effects or objecting strongly to government efforts to make it compulsory. Such doubts have never entirely disappeared, and they still influence public health today. Nevertheless, the overall results have been dramatic. Smallpox, the very disease that Jenner first studied, was declared completely eliminated from the world in 1980—the first, and so far the only, human disease ever to be wiped out by deliberate human effort. For many scientists, it remains the clearest proof of what vaccination can achieve.