Set priorities for vaccine manufacture. The lengthy process of advanced vaccine development and licensure should be reserved for agents for which vaccines are thought to be needed within the next several years. For other agents, secure the scientific underpinnings. The antigen requirements of a modern vaccine will remain relatively unchanged once discovered and well defined, as will the phenotype of a protective immune response. However, the optimal vaccine platforms by which such antigens will be constructed and delivered may change almost as rapidly as computer hardware.