Traditionally, vaccination aims to prevent infectious diseases. It can be considered as one of the most successful medical strategies. The conventional vaccines routinely applied in man are very effective in preventing a number of infectious diseases. This is illustrated by the fact that mass vaccination has resulted in the worldwide eradication of smallpox in the 1970s. Moreover, diphtheria, tetanus, poliomyeli-tis, measles, mumps, and rubella are under control in the developed countries as well as in an increasing number of developing countries, because of the application of childhood vaccines. Currently, vaccines are not only developed against infectious diseases. Vaccines in the pipeline include anti-drug abuse vaccines (nicotine, cocaine) and vaccines against allergies, cancer and Alzheimer’s disease.
In the rapidly evolving field of new vaccine technologies one can discern the improvement of existing vaccines and the development of vaccines for diseases against which no vaccine is available yet. Modern biotechnology has an enormous impact on current vaccine development. The elucidation of the molecular structures of pathogens and the tremendous progress made in immunology during the past few decades have led to the identification of protective antigens and ways to deliver them. Together with technological advances, this has caused a move from empirical vaccine development to more rational approaches. A major goal of modern vaccine technology is to fulfill all requirements of the ideal vaccine as summarized in Figure 1, by expressing antigen epitopes (¼ the smallest molecular structures recognized by the immune system) and/or isolating those antigens that confer an effective immune response, and eliminating structures that cause deleterious effects. Thus, “cleaner,” well-defined products can be obtained, resulting in improved safety. In addition, modern methodologies may provide simpler production processes for selected vaccine components.
In the following section immunological princi-ples that are important for vaccine design are summarized. Subsequently, conventional vaccines, which are not a result of modern genetic or chemical engineering technologies will be addressed. Conventional and modern vaccines are listed in Table 1. Current strategies used in the development and manufacture of new vaccines are discussed in the section “Modern vaccine technologies”. It is not our intent to provide a comprehensive review of all possible vaccine options for all possible diseases. Rather, we will explain modern approaches to vaccine development and illustrate these approaches with representative examples. In the last section pharma-ceutical aspects of vaccines are dealt with.