The principle of vaccination is based upon which property of immune system?

The principle of immunisation or vaccination 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) are introduced into the body. The vaccines generate memory B cells and memory T cells that recognise the pathogen quickly on subsequent exposure to the pathogen and overwhelm the invaders with a massive production of antibodies. These antibodies would neutralise the pathogenic agents during actual infection.