RESUMEN
Since smallpox, vaccine-development programs have varied, yet common elements exist. Investment in vaccine research and development depends on epidemiology, market size, funding, and liability. Fear of liability inhibits innovation, adaptation of existing methods, and regulatory decision-making. Vaccine evaluation proceeds from animal and in vitro studies to controlled human clinical trials. Successive stages provide the information base necessary for decisions on vaccine approval for general use, but sociopolitical forces can affect the process. The World Health Organization establishes nonbinding international norms for vaccine acceptability that are adopted by many countries. Concerns for purity and safety need to be addressed along with cost and vaccine availability. For example, replacement of brain tissue-derived rabies vaccine in developing countries with a continuous cell line-derived vaccine is possible if purity is balanced in relation to safety. Substantially reducing the toll of infectious diseases will require cooperation and common-sense decisions.
