In this article we will discuss about the meaning and types of immunisation.
Meaning of Immunisation:
The birth of immunology as a science may be dated from Edward Jenner’s successful vaccination against small-pox in 1796. The importance of prophylactic immunisation against infectious diseases is best illustrated by the fact that worldwide programmes of vaccination have led to the complete or nearly complete eradication of many of these diseases in developed and developing countries.
The process of producing a state of immunity in a subject is referred to as immunisation.
Vaccination is a type of immunisation in which a harmless or less harmful form of a pathogen is intentionally administered in an individual to induce a specific immune response that protects the individual against later exposure to the same pathogen. Now, immunity can be acquired either by natural processes or by artificial means such as injection of antibodies or vaccines.
Types of Immunisation:
Immunisation, thus can also be classified into two categories:
(1) Passive immunisation
(2) Active immunisation.
1. Passive immunisation:
The acquisition of immunity by receipt of preformed antibodies rather than by active production of antibodies after exposure to antigen is referred to as passive immunisation. For example, it occurs naturally by transfer of maternal antibodies across the placenta to foetus. Passive immunisation through maternal antibodies to diphtheria, tetanus, rubella, mumps, poliovirus and streptococci, afford protection to the developing foetus.
It can also be achieved by injecting preformed antibodies to the recipient. In the past, before antibodies and vaccines became available, passive immunisation provided a major defence against various diseases. Still now, there are certain conditions that require the use of passive immunisation.
For example, (i) in case of immuno deficiency where synthesis of antibody is inhibited or in acquired B cell defects; and (ii) when a disease is already present and the antibody may ameliorate or help to suppress the effects of toxin (tetanus, diphtheria etc.).
However, in all cases, treatment by passive immunisation should be done very carefully to avoid many risks that are frequently associated with such immunisation processes, viz. anaphylaxis, type III hypersensitivity etc.
2. Active immunisation:
Immunisation, that is achieved by natural infection with a microorganism or that can be acquired artificially by administration of a vaccine, is referred to as active immunisation. As the name implies, in this case, the immune system plays an active role—proliferation of antigen- reactive T and B cells results in the formation of memory cells.
Therefore, during subsequent exposure to the pathogenic agent, such immunisation elicits a heightened immune response that successfully eliminates the pathogen or at least prevents disease mediated by its products.
Unlike passive immunisation, whose aim is transient protection or alleviation of an existing condition, the goal of active immunisation is to elicit protective immunity and immunologic memory. Active immunisation with various types of vaccines has played an important role in the reduction of deaths from many infectious diseases throughout the world.