The immune system is the only organ system in the body besides the central nervous systems endowed with memory. Both types of memories are specific and long-lasting, sometimes life long. This memory capacity of the immune system provides the basis for the most cost-efficient of all medical interventions, successful vaccinations against many common infectious diseases. Such a success requires the isolation of the infectious agent or toxic substance, methods to grow and/or purify the relevant antigen and change it into something innocuous whilst maintaining its immunogenicity. Whereas the early...