Three major advances have led to increase in length and quality of human life:increased food production, improved sanitation and induction of specific adaptive immune responses to infectious agents (vaccination). Which has had the most impact is subject to debate.The number and variety of infections agents and the mechanisms that they have evolved to allow them to colonize humans remained mysterious and confusing until the last 50 years. Since then science has developed complex and largely successful ways to immunize against many of these infections.
Six specific immune defense mechanisms have been identified. neutralization, cytolytic, immune complex, anaphylactic, T-cytotoxicity, and delayed hypersensitivity. The role of each of these immune effector mechanisms in immune responses induced by vaccination against specific infectious agents is the subject of this review.
In the past development of specific vaccines for infections agents was largely by trial and error. With an understanding of the natural history of an infection and the effective immune response to it, one can select the method of vaccination that will elicit the appropriate immune effector mechanisms (designer vaccines). These may act to prevent infection (prevention) or eliminate an established on ongoing infection (therapeutic).