By Jenner's time, the practice of smallpox inoculation had become commonplace in England. However it had a major disadvantage: until the infection from inoculation had run its course, the subject was infected, and infectious, with actual smallpox. This made them a risk to any family or acquantainces not already immune.
There was a local folk tradition amongst those who milked cows, that an infection with the so-called `cow-pox' protected one from contracting smallpox. Cowpox was harmless compared to smallpox and Jenner realised that if the folk tradition were true it offered considerable advantages over the use of smallpox in inoculation. He tested cowpox, infecting a boy named James Phipps in the same manner as used in smallpox inoculation, but using material from a cowpox pustule. The boy contracted cowpox, and recovered safely. Jenner then applied the standard smallpox inoculation; the boy was completely unaffected, showing that cowpox had made him immune to smallpox.
Jenner called his method vaccination, as the original infective material came from a cow (Vacca is Latin for a cow). His work was published in 1798.
He was a disciple of John Hunter.
Jenner realised the long-term implications of vaccination, and looked foward to the day when smallpox would no longer be a threat anywhere on earth; his dream eventually reached fruition with the global eradication of smallpox in the late 1970s.
James Phipps' house in Berkeley is now the Jenner Museum.
- Jenner's papers on vaccination are available on line at http://www.bartleby.com/38/4/
- The Jenner Museum has a Web page at http://www.dursley-cotswolds-uk.com/Jenner%20museum.html