Question

Describe the underlying principle of vaccination

Answer 1

The vaccination works b injecting the disease causing bacteria into the body by injection. The human immune system develop the antigens that fights these bacteria and create a memory of this disease in the pathogen which gives protection to this disease by strengthen the immune system. 

Answer 2

Vaccination may be defined as the administration of some agents that mimic the microbe for the protection of the body from communicable diseases. The agent can be a dead or attenuated (weakened or non pathogenic) form of the pathogen.
The principle of vaccination is that the more similar the vaccine is to the natural disease the better is the immune response to the vaccine.