Practical and ethical issues in the development of a vaccine against schistosomiasis mansoni.

Clinical trials to evaluate schistosomal vaccines are in progress. We discuss the desired characteristics of such a vaccine, propose a product profile, and consider the clinical and pre-clinical studies needed for its licensure, within practical and ethical constraints. We believe that licensure of a schistosomal vaccine will be greatly facilitated by resolution of the following issues: identification of the human immunoprotective antigens and mechanisms; induction of the appropriate responses by adjuvanted vaccines; understanding the effect of immunization on immunopathology; development of an improved serologic assay to determine worm burden; generation of approximately $500 million to fund the project; and development of a physical infrastructure with trained professionals in disease-endemic countries to perform Phase III clinical trials. We also believe that development of a schistosomal vaccine, while a long range goal, is possible and desirable, and we have indicated some of the practical steps that will be required to achieve this laudable accomplishment.