What is the purpose of vaccines?
Vaccines, medicines containing a preparation of weakened or dead microbes of the kind that cause a particular disease, are administered to stimulate the immune system to produce antibodies against that disease. They are used to force the body's white blood cells to develop a response to the specific pathogen and rid the body of the invading microorganisms.
Immunization can occur naturally when an untreated microbe in the environment is received by a person who has had no prior exposure to that microbe and, therefore, has no pre-made antibodies for defense.
The immune system of an otherwise healthy individual will eventually create antibodies for the microbe, but this is a slow process and, if the microbe is deadly, there may not be enough time for the antibodies to begin being used to inactivate the microbe before serious symptoms or even death can occur.
Artificial active immunization (vaccination) was created to boost the immune system's abilities to more quickly respond. In this process, the microbe is introduced into the person before they have been exposed to take it in naturally from the environment or directly from an infected person.
Microbes to be used in a vaccine are treated to weaken them (attenuated live vaccines) so that they will not cause disease in the person receiving the vaccination. Depending on the type of microorganism for which immunization is desired, vaccines can be used made from the attenuated pathogen, from entirely inactivated ("dead") microbes, from incomplete particles of the microbe, or treated toxins from the germ.
See the related questions below for more information about vaccinations.
Conventional vaccines consist of whole pathogenic organisms, which may either be killed or live vaccines; the virulence of pathogens is greatly reduced in attenuated vaccines. This is classified into 2 categories :a)Live or attenuated vaccines; (eg : BCG vaccine) b)Inactivated vaccines (eg : Salk polio & Pertussisvaccines)