The vaccine is a preparation intended to produce immunity to a disease by stimulating the production of antibodies. Vaccines are comprised of substances such as suspension of killed or attenuated microorganisms or products or derivatives of microorganisms that can stimulate the immune system. In normal conditions, disease-causing organism induces an immune response in the host. By way of an increase in immune response, the quantity of infections agents gradually reduces due to a gradual rise in immune response, ensuing recovery in physical condition. Immune response against the pathogen is multifold and includes the synthesis of proteins called "antibodies" and the production of " memory cells." The antibodies bind to the disease-causing organisms and lead to their eventual destruction. Memory cells remain in the bloodstream for a long time, times they remain for the host's lifetime.
Memory cells mount a quick protective immune response when the same pathogen reenters into the body. The response shown by the memory cells is often so rapid that infection doesn't develop. Vaccines initiate the production of antibodies and memory cells similar to the natural immune response but without causing any harm to the individual. All the vaccines may not be very safe because of the presence of pathogens or their materials. The safety and effectiveness of a vaccine depend on how it is made and what it contains.
There are six main types of vaccines:-
1) Live virus vaccines
2) Killed or inactivated virus vaccines
3) Subunit vaccines ( purified or recommend viral antigen)
4) Recombinant virus vaccines
5) Anti idiotype antibodies
6) DNA vaccines
LIVE VIRUS VACCINES:-
Live virus vaccines are prepared from attenuated strains that are completely or almost devoid of pathogenicity but can induce a protective immune response. Since a related virus from a different host can not cause disease in the new host, it can also be used in live virus vaccines.
KILLED OR INACTIVATED VIRUS VACCINES:-
Preparation of killed vaccines may take the route of hart or chemicals. These vaccines are prepared by simply inactivating the pathogens. The chemicals used include the virus is formalin.
SUBUNIT VACCINES:-
Subunit vaccines are defined as those containing one or more pure or semi pure antigens. Since the technology for growing viruses to high titers in cell cultures advanced, purifying virus and viral antigens became practicable.
RECOMBINANT VIRAL PROTEINS:-
Virus proteins have been expressed in bacteria, yeast, mammalian cells, and viruses. E. coli cells are the first to be used for this purpose. Still, the expressed proteins are not glycosylated, which is a major drawback, as many viruses' immunogenic proteins are glycosylated.
ANTI -IDIOTYPE ANTIBODIES:-
The ability of anti-idiotype antibodies to mimic foreign antigens has led to their development as vaccines to induce immunity against viruses, bacteria, and protozoa in experimental animals.
DNA VACCINES:-
Recently, encouraging results are reported for DNA vaccines whereby DNA coding for the foreign antigen Is directly injected into the animal. The foreign antigen is directly produced by the host cells.
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