Vaccine is a preparation intended to produce immunity to a disease by stimulating the production of antibodies.

Vaccines comprise substances such as suspensions 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 and by way of increase in immune response, the quantity of infectious agents gradually reduce due to gradual raise in immune response, ensuing recovery in physical condition.

Immune response against the pathogen is multi-fold and includes the synthesis of proteins called “antibodies” and production of “memory cells”. The antibodies binds to the disease causing organisms and lead to their eventual destruction.


Memory cells remain in the blood stream for long time, some times they remain for the life time of the host. Memory cells mount a quick protective immune response when the same pathogen reenters in to 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 with out 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 depends 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 recombinant viral antigen).

4. Recombinant virus vaccines.


5. Anti-idiotype antibodies.

6. DNA vaccines.