The most effective mechanism for the elimination of disease from society is the use of vaccinations, but these often require repeated administration. However, single-administration vaccine formulations provide the repeated administrations automatically. One approach is the development of injectable controlled-release microsphere formulations containing the vaccine antigen that is released as a pulse 1-6 months after injection. The time of the pulse is dependent upon the rate of polymer degradation, which is dictated by the polymer's composition and molecular weight. This controlled-release technology may provide complete protection against disease after a single administration.