Question

how the basis of principle of immunization comeinto wage?

Answer 1

It was found out that when a person was infected with viral diseases such as hepititis A, he aquired immunity against that virus which was found to be due to antibodies that were found against the infection. Same phenomenon was applied to the immunization by scientists who gives a small dose of virus in a human being in form of a vaccine which is sufficient to produce antibodies but not the whole infection, such vaccines by producing antibodies provides immunity to an individual.