In 1796, Edward Jenner successfully used cowpox material to immunize individuals against smallpox, creating the earliest variation of the modern vaccine.
Today, the Centers for Disease Control lists 26 diseases against which vaccines provide immunity.
The herd immunity that vaccinations help create, protecting a community by immunizing a critical mass of the population, has helped eradicate or nearly eradicate diseases including diphtheria, pertussis (whooping cough) and polio.
