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Immunization/Vaccination

Human beings are frequently infected with a variety of pathogens, including bacteria, viruses, fungi, and parasites. A vaccine is a preparation that, when administered, can provide protection against a particular infectious agent. The idea for a vaccine was borne of observations that once an individual had suffered a particular infectious ailment, that person was unlikely to contract that disease again. There are reports dating to 200 b.c. of individuals in India and China inoculating themselves and others with infected matter from those suffering with mild cases of smallpox. Much later, Edward Jenner observed that milkmaids who had come into contact with cowpox did not develop smallpox when exposed. He subsequently tested this observation by directly exposing individuals to the fluid from cowpox lesions and then challenging them with a controlled infectious exposure, or inoculation, of smallpox. His test subjects did not become ill with smallpox, providing preliminary validation of the concept of vaccination.

Ultimately, vaccination seeks to expose the immune system to a weakened, killed, or fragment of a pathogen in a way that generates an immune response so that upon exposure to that actual pathogen there is a rapid removal of the pathogen. This rapid response ultimately will prevent spread of the invading organism from the portal of entry and would also prevent subsequent replication and disease manifestations.

The Immune System

A basic understanding of the immune system helps to clarify the importance and problems inherent in vaccinations. When the body is exposed to a pathogen the body responds in several ways. There are components of the innate immune system that react to whatever pathogen gains entry into the body. The innate immune system reaction is rapid, but is nonspecific and confers no “memory” meaning that if the body is exposed to the same pathogen again the response is not faster nor stronger the second time. There are several cell types that are involved in the innate immune response including mast cells, neutrophils, basophils, eosinophils, dendritic cells, and neutrophils. While these cells all have specific functions, they have the capacity to kill a broad range of infecting organisms. Innate immunity is a more primitive response, and there are similar defense mechanisms in not only humans, but all plant and animal life.

In contrast, the adaptive immune system is composed of several different cell types, including B cells which are responsible for making antibodies. Antibodies recognize specific features of an infectious organism, and by binding, can promote the sequestration, removal or engulfment of that pathogen. T-cells can help direct the immune system and can also directly kill cells of the body that are infected with a pathogen. It takes longer for the adaptive immune system to respond to an infectious agent. However, upon exposure to a bacteria or virus there is concurrently the process of eliminating the offending agent and also the development of “memory” cells. These memory cells, both B and T-cells, have been exposed to a particular infectious agent so that upon a second exposure there is a more rapid and specific response that can clear the body of that particular infection before it has a chance to cause disease. Oftentimes there is a cumulative response, in that a single exposure does provide some level of memory and protection, but multiple exposures are needed to develop a high level of immunity. The process of immunization takes advantage of the ability of the immune system to remember an infection and become more prepared to clear a subsequent infection.

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