ALL ABOUT VACCINES
Immunity, as defined by the Centre for Disease Control is "the ability of the human body to tolerate the presence of material indigenous to the body (self), and to eliminate foreign (non-self) material."
The discriminatory ability of the immune system to identify a microbe as foreign provides the body with protection from infections. Immunity to a microbe is usually indicated by the presence of antibodies to that organism.
Immunity can be gained either passively or actively. Both can either be natural or acquired:
◎ PASSIVE IMMUNITY refers to the process whereby a person is given antibodies to protect against infection; this is an immediate but short lived protection (weeks to months).
○ Natural Passive Immunity: involves the transfer of maternal antibodies across the placenta.
○ Acquired passive immunity: refers to the process of obtaining serum from immune individuals, concentrating the antibodies and then using the concentrated serum to protect a potentially infected person; examples include the rabies and tetanus antitoxins.
◎ ACTIVE IMMUNITY refers to the process whereby a person’s immune system is stimulated to make its own antibodies. Active immunity is long-lasting and often life-long.
○ Natural active immunity: Survive an infection. Following exposure of the immune system to an antigen (a foreign substance or toxin), certain cells (B-lymphocytes) tag the antigen as foreign and then secrete antibodies which attack and neutralize it. Other cells of the immune system (phagocytes and T-lymphocytes) are also recruited to then destroy and remove the antigen. With a few exceptions, survivors of an infection will have lifelong immunity to that disease. If re-exposed to the same antigen/infection, the immune system will "remember" (immunologic memory) and kick in to re-establish protection.