What is Vaccination and Immunization?
During a lifetime a person becomes naturally immune to various types of infections due to natural exposure to them. But often such infections tend to be mild or subclinical. There may occur a severe form of infection leading to a fatal form of consequence. Immunity will develop slowly and only if the victim survives the attack. It would be much better if we do not take a chance of natural immunity but take measures to immunize our body early in life through artificial immunization. It will eliminate the risk of coming in contact with highly infectious pathogens later in life when it may take a longer period to develop immunity and by the time the body acquires immunity the person may die.
In view of the need, man has devised means of developing specific immunity artificially and safely. The process is a natural one but is used under modified and carefully controlled conditions and is therefore called artificial immunization or vaccination.
In artificial immunization, a person’s body is stimulated to develop resistance through injection or infection of certain kinds of antigenic substances such as exotoxin of certain infectious bacteria or their dead or ‘attenuated’ form (bacteria of which virulence is reduced by some process is called attenuated). The exotoxin, dead or avirulent form of bacteria do not cause any disease but induce the formation of specific antibodies against the antigen carried by such infectious bacteria. Artificial immunization against poliomyelitis, yellow fever, measles, smallpox, diphtheria, etc. is available today which is administered early in life to offer long-term immunity.
A person who naturally develops antibodies through accidental exposure to infection does not become immune to such infections for entire life because the antibodies so formed must be restimulated for providing long-term immunity. Renewed contact with each infectious agent has no outwardly
perceptible effect but inwardly and unseen it restimulates the production of specific antibodies. Thus repeated stimulation by antigenic substances serves to maintain immunity.
The protective effect of repeated stimulation of antibodies is exploited in the artificial process by giving booster doses, one year after a primary stimulus is given to a child. The effect of primary stimulus in maintaining antibody titers gradually diminishes. But a second stimulus in the form of a booster dose immediately increases the antibody titers. This is rather a recall reaction or anamnestic reaction. This indicates that although after the primary stimulation the antibody titers gradually decline the physiological response persists which can be recalled to form adequate antibody titers to protect the body against vigorous attack in the future.