The goal of vaccines to artificially
induce a primary immune
response (and consequent formation
of antibodies memory cells)
concerning a infection or disease
in to immunize the individual
infections by the pathogenic
in the future.

Since antibody does not act
variety of antigens but
it actsonly against its antigen,
it is necessary the immune system
to contact in some way the
antigen against which immunization
is wanted. The of
specific molecular portions each
antigen causes the system to
produce the variable portion of
the to attack that
antigen. to induce the active
it is necessary to
into the body small of
the infectious agent the agent
entirely (dead inactivated).