Future approaches to vaccine development: single-dose vaccines using controlled-release delivery systems.

The development of single-dose vaccines, mainly those administered during childhood, which would effectively protect against certain diseases, would be a very important advance towards better immunization coverage and protection against the respective pathogens. Biodegradable polymeric microspheres which are 'programmed' to deliver the antigen when a boost of the immune response is required, may be a possible way of achieving this goal.