Why vaccines fail: Is there a genetic basis?
Infectious disease remains the single most common cause of premature death in the world today even though immunization has been shown to be one of the most effective public health intervention strategies available for the prevention of microbial infection. The existence of microbes some 3 billion years before humans and the co-evolution of humans in an environment predominated by microbes has resulted in highly complex survival relationships. As a consequence, the causes of vaccine failure are also many, complex and interrelated. This complexity has been matched by a plethora of approaches to develop new and more effective vaccination strategies. Vaccine failure against a specific infectious disease can be related to various technical, microbe and host factors. Technical factors predominantly include failures to comply with cold chain requirements or regime guidelines. Vaccine failure due to microbial factors primarily relates to subtype replacement. There have been no reports of failure due to vaccination selection pressure or microbial polymorphism. Host factors can be divided into 2 categories. First, environmental factors are those which affect the general well being of an individual and hence their ability to mount an effective immune response [eg nutritional status, stress]. Secondly, the non-responsiveness observed in some subjects to otherwise efficient generic vaccines has been linked to genetic factors. The linkage between the variability in vaccine responses and polymorphism in the development of immune responses will be discussed.