Naturally Acquired Immunity
As early as 2500 years ago in Greece, some people understood enough about contagion to know that a person who had recovered from plague would not get it again. Later,
physicians recognized that a person acquires immunity to many diseases in this way.
This protection comes from another special cell of the immune system. Whenever B cells and T cells are summoned, they transform some of their numbers into memory cells.
Although the army of antibodies necessary to destroy an infectious agent does not remain, the memory cells do. If the memory cells recognize the invader again, the
immune system quickly mounts a defense and defeats the interlopers before illness can occur. This type of immunity is naturally acquired. Most of us benefit from
naturally acquired immunity from our earliest days. Certain types of immune cells are passed from mother to fetus during pregnancy. Thus, most newborns, though
vulnerable in many ways, have a head start in fighting disease.
Artificially acquired immunity can be either passive or active. Artificially acquired passive immunity results when antibodies produced by another animal or human are
given to someone to prevent or treat disease. For example, administering tetanus antitoxin or rabies immune globulin to someone is a way of conferring passive immunity.
This type of immunization is effective very quickly, but since it lasts only a short time, it is used to protect people when they are particularly vulnerable, such as
immediately after exposure to a serious disease. Artificially acquired active immunity, the type obtained from vaccines, is essentially the subject of this booklet.
Artificially acquired active immunity is achieved through safe and effective vaccines. Traditional vaccines are preparations of killed or weakened bacteria or viruses,
or parts of these microbes, or inactivated toxins from the disease-causing agent. Recently, innovative vaccine technologies have revealed many more ways to give people
active immunity to a disease. These include subunit vaccines, conjugate vaccines and naked DNA vaccines.
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