Impediments to the development of additional vaccines: vaccines against important diseases that will not be available in the next decade.

The availability of new biotechnologies has led to the prediction that new or improved vaccines can be developed for 27 diseases within the next decade. The reasons why such optimism cannot be extended to the availability of vaccines for many other infectious diseases are considered by reviewing the steps in vaccine development, from identification of the etiologic agent to construction of attenuated or inactivated vaccines. Impediments to development may exist or arise at any point in this pathway (e.g., multiplicity of serotypes, inability to cultivate the pathogen, multistage life cycles with multiple antigens, unpredictability of epidemics, inadequate knowledge of pathogenesis and immunity, fear of gene splicing, need for an adjuvant, and lack of profitability). Diseases for which vaccines are not likely to be available in the next decade include trachoma, onchocerciasis, pneumonia due to Legionella and to mycoplasmas, amebiasis and giardiasis, schistosomiasis, syphilis, chlamydial urethritis, trypanosomiasis, leishmaniasis, and filariasis, and non-A, non-B hepatitis.