A vaccine is either a cell suspension or a by product secreted by the cell which, when introduced into the body, stimulates the production of antibodies.Serum is used for obtaining antibodies.The introduction of harmless antigenic material into healthy person for providing acquired immunity against the disease is known as immunisation or vaccination.
The principle of immunisation or vaccination is based on the property of ‘memory’ of the immune system. In the process of vaccination, a preparation of antigenic proteins of pathogens or inactivated/weakened pathogens (vaccine) is introduced into the body. These antigens generate the primary immune response and the memory B and T-cells.
When the vaccinated person is attacked by the same pathogen, the existing memory T or B-cells recognise that antigen quickly and counter the invaders with a massive production of lymphocytes and antibodies.
What are the Types of Vaccination ?
These are of following types :–
(i) Toxoids :-
The toxins produced by certain organisms are inactivated and are used in the preparation of vaccines. These vaccines provide passive immunity for short period.
tetanus, diphtheria vaccines.
(ii) Live vaccines or Attenuated vaccines :-
These vaccines are prepared from live generally attenuated, in which the pathogen is weakened to make it non-virulent organisms.
OPV (Oral Polio Vaccine, developed by J Sack in 1952), BCG (Bacillus Calmette Guerin), for tuberculosis, smallpox, yellow fever and influenza vaccines. These vaccines provide active life long immunity.
(iii) Killed vaccines or Inactivated vaccines :–
Such vaccines are prepared by killing the pathogenic organisms by heat or ultraviolet rays or alcohol/formalin or phenol.
typhoid vaccine, polio vaccine, typhus vaccine, cholera vaccine, rabies vaccine, plague vaccine.
(iv) Combinations :-
If more than one kind of immunising agent is included in the vaccine, it is called a mixed or combined vaccine.
Some of the well-known combinations are as follows :
DPT [Diphtheria + Pertussis (whooping cough) + Tetanus],
DT (Diphtheria + Tetanus),
DP (Diphtheria + Pertussis),
Tetanus + Influenza,
MMR (Measles + Mumps + Rubella),
Measles + Rubella.
What is Classification of Vaccination ?
Vaccines are classified under following categories :–
(i) First generation vaccines :-
These vaccines are produced by conventional ways in which whole microorganisms are used. These are not of uniform quality and produce side effects.
(ii) Second generation vaccines :–
These vaccines do not contain the whole microorganism, but their subunits are present.
hepatitis-B virus vaccine, herpes virus vaccine, pneumonia vaccine.
(iii) Third generation vaccines :-
These vaccines are produced by genetic engineering. These are chemically synthesised multivalent vaccines. These vaccines have high purity. Vaccine against diphtheria toxin developed by Audibert et. al. 1981, leukaemia virus vaccine. Some of the vaccines under preparation are against malaria, leprosy, hepatitis-C, AIDS, etc. are under study.
The first vaccination was carried out by a British physician, Edward Jenner (1796) to protect people from smallpox.The first true vaccine against chicken cholera was developed in 1880 by Louis Pasteur.
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