Provide information about vaccination.

(N/A) The principle of vaccination or immunization is based on the property of 'memory' of the immune system. In vaccination,a preparation of antigenic proteins of pathogen or inactivated/weakened pathogen (vaccine) is introduced into the body.
The antibodies produced in the body against these antigens neutralize the pathogenic agents during actual infection. The vaccines also generate memory $B$ and $T$-cells that recognize the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies.
If a person is infected with some deadly microbes to which quick immune response is required,as in tetanus,we need to directly inject the preformed antibodies or antitoxin (a preparation containing antibodies to the toxin).
Even in cases of snakebites,the injection given to the patient contains preformed antibodies against the snake venom. This type of immunization is called $passive$ $immunization$.
Recombinant $DNA$ technology has allowed the production of antigenic polypeptides of pathogen in bacteria or yeast. Vaccines produced using this approach have been made on a large scale and have been increasingly available for immunization,e.g.,Hepatitis-$B$ vaccine produced from yeast.