Chapter 7 : Edward Jenner and the Discovery of Vaccination

Abstract:

Understanding the theories about smallpox in the 18th century helps to explain what Edward Jenner and others were up against in order to hypothesize, test, and prove the theory of vaccination to a skeptical and critical medical world. Jenner invented the phrase variolae vaccinae to support his notion that the diseases smallpox and cowpox were related. His book, An Inquiry into the Causes and Effects of the Variolae Vaccinae, had three parts. The first part discussed what Jenner considered to be the origin of cowpox, a hypothesis that was quickly discredited. The second part discussed the hypothesis that cowpox protects against smallpox. Importantly, he used material from the deliberately induced cowpox infection in one person to vaccinate another case. He concluded by stating that cowpox protects the human constitution from the infection of the smallpox. Jenner believed that vaccination was safer than variolation and that the protection imparted by cowpox vaccination would be lifelong. The technique that Jenner used, placing material from a cowpox pustule into cuts in the forearm, was discarded in 1858 in favor of the use of lancets, the technique still in use for smallpox vaccination. Within 10 years of its inception, vaccination had reached around the globe. Vaccinia virus represents a hybrid virus whose precise origin is unclear but which likely arose from inadvertent mixing of cowpox and smallpox viruses in those early days of vaccination. Genetically, vaccinia virus is more closely related to smallpox than cowpox virus.