Inoculation | Research & Encyclopedia Articles

Inoculation

Inoculation refers to the injection of dead or weakened disease-causing bacteria or viruses into the human body in order to produce immunity against that disease. The use of inoculation to prevent disease most likely started with smallpox, a dreaded disease first named variola, in 570 A.D. In the ninth century, smallpox was differentiated from measles by a noted Persian physician, Rhazes. Historical accounts mention that epidemics of smallpox raged in many parts of the world.

It is thought that perhaps, thousands of years ago in China, doctors would remove pus and scabs from people who were suffering from smallpox. They would put the mixture into scratches made on a healthy person's arm, a procedure later called variolation or scarification. Then the healthy person would get the disease, only mildly, and would thereafter have immunity against smallpox. A problem arose some of the time when the inoculated person contracted a serious case of the disease and died. For years, this technique of scratching smallpox fluid onto healthy people had been used in China, India, and Turkey. The idea of variolation was introduced to Britain and western Europe in 1717 by an English author, Lady Mary Wortley Montagu (1689-1762). As the wife of the English ambassador to Constantinople, Lady Montagu had her three-year-old son variolated, as was the practice in Turkey. In the United States, Zabdiel Boylston may have been the first to have his son and two slaves inoculated, in 1721.

In eighteenth-century Europe, smallpox had spread throughout the land, and one in ten persons died of the disease, most of them children. Common folk wisdom spread the idea that anyone who contracted the bovine disease cowpox, a similar, milder disease, became immune to human smallpox. In 1796, Edward Jenner, an English physician who knew of the practice of variolation, decided to test an idea. He took some cowpox fluid from the sores of a milkmaid named Sarah Nelmes and rubbed it into cuts on the arm of an eight-year-old boy named James Phipps. A few days later, Jamie came down with a mild case of cowpox, but soon got over it. Six weeks later, Jenner gave Jamie some fluid that was taken from a person who had smallpox, and the boy was not affected. The boy had gained immunity from the inoculation. To describe the inoculation, Jenner coined the term vaccine from vacca, Latin for cow and vaccinia, Latin for cowpox.

With the success of his vaccine, Jenner was awarded a sum of money to continue his work, and soon thousands of English citizens were vaccinated, including the royal family. The practice spread to Germany and Russia. Then U.S. President Thomas Jefferson wrote to Jenner congratulating him on his success, and when Jenner's vaccination was made available in America, Jefferson insisted that members of his family get vaccinated against smallpox. Jefferson praised Jenner for having found a way to rid humanity of smallpox. For half a century, smallpox remained the only disease for which there was a vaccine.

Attitudes about disease prevention did change slowly during the 1800s, when people began to realize that filthy living conditions, dirty drinking water, and the lack of proper disposal of human waste could be associated with outbreaks of disease. Pioneers in health care--including Florence Nightingale, a nurse, and Sir Joseph Lister, a surgeon--brought on the sanitary movement, calling for clean instruments and bedding in hospitals. The practice of scarification became more widespread with the use of a "scarificator," a device with small pointed knives used for bleeding and for injecting smallpox vaccine into the skin.

In the mid-nineteenth century, French chemist and microbiologist Louis Pasteur was developing the germ theory, which states that specific microorganisms cause specific diseases. During one series of experiments, Pasteur cultured cholera bacteria and inoculated healthy chickens with the bacteria. When the chickens failed to get cholera, Pasteur was surprised, but he later realized that the bacteria had gotten old and lost some of its virulence. Instead of getting the disease, the chickens received immunity against cholera. This convinced Pasteur that weakened germs would be ideal for a vaccine. They would not be strong enough to cause a serious case of the disease, but strong enough to confer immunity. After a German doctor, Robert Koch, isolated the bacteria that cause anthrax, a deadly disease in livestock, Pasteur set to work on finding a suitable vaccine. With the aid of his assistant, Pierre-Paul-Emile Roux, Pasteur worked on weakening or attenuating the virulence of the bacteria so that an inoculation of it could bring about immunity without producing a serious case of the disease. They met with success, and so cases of anthrax in animals and "woolsorters' disease" in humans came under control. Later in his career, Pasteur successfully developed a series of inoculations to prevent rabies using tissue from the brains and spinal cord of rabid rabbits.

Roux continued his work in bacteriology, concentrating on the disease diphtheria. He found that not only did a specific bacilli bacteria cause diphtheria, but it was a toxin (poison) produced by the bacteria that caused disease symptoms. Once the concept of toxins was established, bacteriologists sought antitoxins to neutralize the harmful effects of toxins as cures for specific diseases.

Today children in the United States are routinely vaccinated against a number of diseases, including hepatitis B, diphtheria, tetanus, pertussis, H. influenzae type B, polio, measles, mumps, rubella, and chickenpox. Travelers may also need to be vaccinated against diseases such as yellow fever before entering certain countries. New vaccines continue to lead to dramatic drops in the incidence of serious diseases. For example, the number of cases of H. influenzae type B meningitis in the United States has dropped 95 percent among infants and children since the vaccine was introduced in 1988.