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Artificial immunity is a means by which the body is given immunity to a disease through intentional exposure to small quantities of it. The most common form of artificial immunity is classified as active and comes in the form of vaccinations, typically give to children and young adults. The passive form of artificial immunity involves introducing an antibody into the system once a person has already been infected with a disease, ultimately relieving the present symptoms of the sickness and preventing re-occurrence.
The first record of artificial immunity was in relation to a disease known as smallpox. Individuals were exposed to a minor strain of smallpox in a controlled environment. Once their bodies built up a natural immunity or resistance to the weakened strain of smallpox, they became much less likely to become infected with the more deadly strains of smallpox. In essence, patients were given the disease in order to help fight it later in life. Although this method was an effective one, the scientists of the time had no real scientific knowledge of why it worked.
Louis Pasteur was the famous inventor who created the germ theory of diseases. His work showed that diseases are often carried by bacteria and that once the bacteria entered the body, there were several natural reactions that would begin to fight them off. Once the body had successfully rid itself of the disease, a second infection with the same bacteria would prove harmless. Pasteur's theories proved that once the body learns to fight specific diseases, it is then able to prevent reinfection on its own.
One of the biggest complications with Pasteur's theory of creating artificial immunity was that certain diseases, such as smallpox, were caused by strains of bacteria that were able to mutate themselves slowly over time. The mutability of these bacteria often resulted in the need for multiple vaccinations. As the bacteria underwent major changes, a new vaccine would have to be developed to give people the ability to fight new strains. This is the primary reason that common diseases, such as influenza, often require a new vaccination every year.
With regards to passive artificial immunity, there are some diseases, such as tetanus, that are only able to be vaccinated on a short-term basis. Unlike a smallpox vaccination that can potentially protect the body from smallpox indefinitely, a tetanus vaccination only provides artificial immunity for a period of around seven years. The bacteria causing the disease itself does not necessarily mutate as it does with influenza; rather, the immunity the vaccination creates has a limited period of effectiveness.