It was 268 years ago today, on 17 May 1749, that Edward Anthony Jenner was born in Berkeley, Gloucestershire, as the eighth of nine children. His father, the Reverend Stephen Jenner, was the vicar of Berkeley, so Jenner received a strong basic education.
He went to school in Wotton-under-Edge and Cirencester. During this time, he was inoculated for smallpox, no doubt by a method close to the one propagated by Lady Mary Wortley Montagu.
At the age of 14, he was apprenticed for seven years to Daniel Ludlow, a surgeon of Chipping Sodbury, South Gloucestershire, where he gained most of the experience needed to become a surgeon himself. In 1770, Jenner became apprenticed in surgery and anatomy under surgeon John Hunter and others at St George's Hospital. William Osler records that Hunter gave Jenner William Harvey's advice, very famous in medical circles (and characteristic of the Age of Enlightenment):
Don't think; try.
Hunter remained in correspondence with Jenner over natural history and proposed him for the Royal Society. Returning to his native countryside by 1773, Jenner became a successful family doctor and surgeon, practising on dedicated premises at Berkeley. He also became a master mason on 30 December 1802, in Lodge of Faith and Friendship #449.
Like any other doctor of the time, Edward Jenner carried out variolation to protect his patients from smallpox. However, from the early days of his career Edward Jenner had been intrigued by country-lore which said that people who caught cowpox from their cows could not catch smallpox. This and his own experience of variolation as a boy and the risks that accompanied it led him to undertake the most important research of his life. Cowpox is a mild viral infection of cows. It causes a few weeping spots (pocks) on their udders, but little discomfort. Milkmaids occasionally caught cowpox from the cows. Although they felt rather off-colour for a few days and developed a small number of pocks, usually on the hand, the disease did not trouble them.
By 1768, English physician John Fewster had realised that prior infection with cowpox rendered a person immune to smallpox. A similar observation had also been made in France by Jacques Antoine Rabaut-Pommier. In the years following 1770, at least five investigators in England and Germany successfully tested a cowpox vaccine in humans against smallpox. For example, Dorset farmer Benjamin Jesty successfully vaccinated and presumably induced immunity with cowpox in his wife and two children during a smallpox epidemic in 1774, but it was not until Jenner's work that the procedure became widely understood. Jenner may have been aware of Jesty's procedures and success.
Noting the common observation that milkmaids were generally immune to smallpox, Jenner postulated that the pus in the blisters that milkmaids received from cowpox (a disease similar to smallpox, but much less virulent) protected them from smallpox.
In May 1796 a dairymaid, Sarah Nelmes, consulted Jenner about a rash on her hand. He diagnosed cowpox rather than smallpox and Sarah confirmed that one of her cows, a Gloucester cow called Blossom, had recently had cowpox. Edward Jenner realised that this was his opportunity to test the protective properties of cowpox by giving it to someone who had not yet suffered smallpox.
He chose James Phipps, the eight-year old son of his gardener. On 14th May he made a few scratches on one of James' arms and rubbed into them some material from one of the pocks on Sarah's hand. A few days later James became mildly ill with cowpox but was well again a week later. So Jenner knew that cowpox could pass from person to person as well as from cow to person. The next step was to test whether the cowpox would now protect James from smallpox. On 1st July Jenner variolated the boy. As Jenner anticipated, and undoubtedly to his great relief, James did not develop smallpox, either on this occasion or on the many subsequent ones when his immunity was tested again. So, in addition to the name of Edward Jenner, we also need to acknowledge the following names for their contribution to this success: Sarah Nelmes (the milkmaid), James Phipps (the child - guinea pig), The gardner Mr Phipps (for allowing this experiment on his son), and Blossom, the Gloucester Cow, for donating the virus. You can still have a look at Blossom, by the way. Her hide is on display at Saint George's University. 
Phipps was the 17th case described in Jenner's first paper on vaccination. Donald Hopkins has written,
"Jenner's unique contribution was not that he inoculated a few persons with cowpox, but that he then proved [by subsequent challenges] that they were immune to smallpox. Moreover, he demonstrated that the protective cowpox pus could be effectively inoculated from person to person, not just directly from cattle.
Jenner successfully tested his hypothesis on 23 additional subjects.
Jenner continued his research and reported it to the Royal Society, which did not publish the initial paper. After revisions and further investigations, he published his findings on the 23 cases. Some of his conclusions were correct, some erroneous; modern microbiological and microscopic methods would make his studies easier to reproduce. The medical establishment deliberated at length over his findings before accepting them. Eventually, vaccination was accepted, and in 1840, the British government banned variolation – the use of smallpox to induce immunity – and provided vaccination using cowpox free of charge.
In 1803 in London, he became president of the Jennerian Society, concerned with promoting vaccination to eradicate smallpox. The Jennerian ceased operations in 1809. In 1808, with government aid, the National Vaccine Establishment was founded, but Jenner felt dishonoured by the men selected to run it and resigned his directorship. Jenner became a member of the Medical and Chirurgical Society on its founding in 1805 (now the Royal Society of Medicine) and presented several papers there. Jenner was also elected a foreign honorary member of the American Academy of Arts and Sciences in 1802, and a foreign member of the Royal Swedish Academy of Sciences in 1806. Returning to London in 1811, Jenner observed a significant number of cases of smallpox after vaccination. He found that in these cases the severity of the illness was notably diminished by previous vaccination. In 1821, he was appointed physician extraordinary to King George IV, and was also made mayor of Berkeley and justice of the peace. He continued to investigate natural history, and in 1823, the last year of his life, he presented his "Observations on the Migration of Birds" to the Royal Society.
Jenner was found in a state of apoplexy on 25 January 1823, with his right side paralysed. He never fully recovered and eventually died of an apparent stroke, his second, on 26 January 1823, aged 73. He was buried in the Jenner family vault at the Church of St. Mary's, Berkeley, Gloucestershire. Jenner was survived by one son and one daughter, his elder son having died of tuberculosis aged 21.