In 1796 the English physician Edward Jenner showed that inoculating a boy with material from a cowpox lesion protected him against subsequent exposure to smallpox, demonstrating the first deliberate vaccine. The practice spread rapidly through Europe and beyond, and in the nineteenth century Louis Pasteur extended the principle to rabies and other diseases, establishing immunisation as a general method. Over the following two centuries vaccines were developed against diphtheria, polio, measles and many other infections. Smallpox itself was declared eradicated in 1980.
Vaccination sharply cut deaths from epidemic disease, helping make crowded urban living survivable and sustaining the population growth that filled the rapidly expanding industrial cities of the nineteenth and twentieth centuries.
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