Some of the early discoveries that led to today’s vaccines happened almost by chance. The astute observations of Edward Jenner and Louis Pasteur were the foundation of modern immunology.
Edward Jenner and the First Vaccine (1790s)
Edward Jenner’s legacy was a vaccination for smallpox; a disease greatly feared during his lifetime. Smallpox killed a third of those who caught it, and the individuals who did survive were often badly disfigured.
Jenner was a physician who practiced in the rural English countryside. Being a country doctor, he was familiar with the region’s medical old wives tales, one of which was that milkmaids who had caught cowpox never became infected with the more serous smallpox.
Cowpox was a mild disease evidenced by discomfort, aching, pustules, some swelling; symptoms that only lasted a few days. In contrast, smallpox was a very serious disease that results in massive disfigurement, sometimes blindness, and often death.
Jenner suspected a connection between the fact that milkmaids were commonly known to get cowpox, but not smallpox. He decided to test this theory by placing the scab from a cowpox lesion into a cut made in the arm of a young man. He then deliberately injected his human guinea pig with smallpox. The infected young man became ill, but after a few days made a full recovery with no side effects.
At first his peers doubted the safety and efficacy of his treatment, and Jenner was publicly humiliated when he presented his findings in London. But eventually the value of the cowpox inoculum could not be denied and Jenner’s discovery changed the world.
Pasteur’s Attenuated Vaccines (1870s)
Physicians of the time observed that individuals who recover from an infectious disease are sometimes immune from future attacks of the same illness. This knowledge prompted Louis Pasteur, a French biologist and chemist, to try to find a way to prevent fowl cholera, an infectious disease of chickens.
Pasteur understood that different microorganisms were associated with different diseases, and had learned how to grow some of them in the laboratory; purposefully infecting animals in order to study the disease.
When a colleague of Pasteur’s postponed inoculations of cholera into a group of chickens, a remarkable discovery resulted. The cholera, which had been left to grow under laboratory conditions for an extended time, no longer could cause the disease. Instead, inoculation with these neglected cultures made the chickens immune to fowl cholera.
By leaving the microbes uncared for in the laboratory media for an extended period of time, the organisms had been weakened or attenuated. Pasteur concluded that inoculation with weakened microbes could render immunity to the disease that that particular microbe caused.
Pasteur then experimented with modifying other organisms such as anthrax, and the virus causing rabies. Ultimately, through his experimentation he created the inoculation procedures of acquired immunity-what we now know as vaccinations.
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