Write the events that take place when a vaccine for any disease is introduced into the human body.

Vaccine is an antigen protein of pathogens or inactivated or weakened pathogens or their toxin. When it is introduced into the body of a person who is required to be made immune it stimulates the production of antibody and memory cell which is called primary response. It does not cause harm when this pathogen enters second time. These memory cells show rapid and massive responses so body become immune to this pathogen.

The vaccine contains proteins of pathogen or inactivated/weakened pathogen. When a dose of vaccine is introduced into the human body, it behaves as an antigen and the body produces antibodies in response to the antigen. This response generates active immunity. The antibodies thus produced will neutralise the pathogenic agents during actual infection. The vaccines also generate memory B- and T-cells that recognise the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies.