Edward Jenner was born on May 17, 1749, in Berkeley, Gloucestershire, England. He grew up in a rural area and developed an interest in medicine from an early age. Jenner is best known for his pioneering work on the smallpox vaccine, which marked the beginning of the field of immunization.

During Jenner's time, smallpox was a deadly disease that claimed many lives. Jenner observed that milkmaids who had contracted cowpox, a milder disease, seemed to be immune to smallpox. This led him to hypothesize that exposure to cowpox could protect against smallpox.

In 1796, Jenner performed an experiment on a young boy named James Phipps. He took material from a cowpox sore on a milkmaid and inoculated Phipps with it. After recovering from cowpox, Jenner exposed Phipps to smallpox and found that he did not develop the disease. This experiment demonstrated the efficacy of the smallpox vaccine.

Jenner's discovery of the smallpox vaccine revolutionized the field of medicine. His work laid the foundation for the development of other vaccines and the eradication of smallpox globally. Jenner's vaccine was effective and safer than previous methods of smallpox prevention, such as variolation.