Jenner was born in Berkeley, England, the third son and youngest of six children of Stephen Jenner, a clergyman of the Church of England. He was orphaned at age five and was raised by his older brother, also a clergyman. When Jenner was thirteen years old, he was apprenticed to a surgeon. Then in 1770, he moved to London, England, to work with John Hunter (1728-1798), an eminent Scottish anatomist and surgeon who encouraged Jenner to be inquisitive and experimental in his approach to medicine. Jenner returned to Berkeley in 1773, and set up practice as a country doctor. His curiosity about natural phenomena and dedication to medicine ultimately earned him status as a pioneer of virology and immunology, as well as the founder of the practice of vaccination.

During and prior to Jenner's lifetime, smallpox was a common and often fatal disease worldwide. Many centuries before Jenner's time, the...