Immunization

Immunization is a method of helping the body's natural immune system be able to resist a particular disease. It is usually carried out by giving someone a mild version of the disease. This allows the body to make antibodies that will resist the disease in the future. Active immunization, or vaccination, has proven to be a highly successful method of disease prevention.

Long before modern science discovered the causes of disease, it was folk practice in some parts of the world to give a powder made from the scabs of recovering smallpox patients to healthy children in the belief that it would somehow protect them in the future. If this risky custom, which originated in China, did not kill the child, it often did grant him or her immunity against a full-blown case of smallpox (a highly infectious viral disease). This same idea was at work when the English physician Edward Jenner (1749–1823) decided to try a dangerous experiment. He based his experiment on the fact that people who had suffered a case of the less serious cowpox (a contagious skin disease found in cattle) often did not catch the deadly smallpox. In 1796 Jenner prepared what he called a vaccine (because the cowpox virus name was "vaccinia") and gave it to a young boy. Months later, he injected real smallpox into the boy. Fortunately, the boy did not get the disease.

This marked the modern beginnings of immunization. Jenner, however, made no claims that he understood why immunization worked. It was not until a century later that the French chemist and microbiologist (a person specializing in the study of microorganisms) Louis Pasteur (1822–1895) proved experimentally that disease-causing microorganisms (organisms that can only be seen through a microscope) that were "attenuated," or weakened, would create an immune response in a person without actually causing the disease itself. On the basis of this breakthrough, active immunization began. It is now known that immunization uses the mechanisms of the body's natural immune system to protect the body against future diseases.

IMMUNIZATION AND ANTIBODIES

In the twentieth century, science learned that the body produces substances called antibodies. These fight and kill what the body recognizes as foreign invaders (disease-producing microorganisms). These antibodies are specific to that particular disease and will remain in the body's "memory cells" for a long time, ever ready to fight should the body recognize the disease in the future.

Today, many viral vaccines are made from live, weakened viruses, including those for yellow fever, measles, mumps, rubella, and polio. Using a live form means that the body will react with a very strong immune response to the particular virus, thereby protecting the individual against future infection. Other vaccines, like rabies, flu, and intravenous polio, use dead viruses and do not confer as strong a protection.

PASSIVE IMMUNIZATION

All of the above are considered to be forms of active immunization, but there is also another method called passive immunization. This method is used when a quick response to a disease is required. Passive immunization consists of injecting specific antibodies into a person to fight a specific disease. For example, a person who is bitten by a snake or who has been exposed to hepatitis cannot wait for his own system to build up antibodies against them. Instead, the person is given a direct and immediate dose of the antibodies in order to neutralize the venom or to kill the microorganism. While passive immunization usually works, it is not long-lasting like active immunization and usually will not protect the person in the future.

IMMUNIZATION WORKS

Immunization has proven to be the safest, least expensive, and most effective means of protecting people against contagious diseases. In many ways it is ideal, since it prevents the disease rather than trying to cure it once it has taken hold. Today, immunization in the developed world has nearly eliminated the threat of typical childhood diseases like measles, mumps, rubella, whooping cough, and polio. In 1980 the World Health Organization declared that smallpox was the first disease to be totally eradicated (destroyed) worldwide.

[See alsoAntibody and Antigen; Immune System; Vaccine ]