Vaccines have been used almost exclusively to prevent or control infectious diseases with the aim of long-lasting immunity. Some, composed of attenuated viruses, have been highly successful and this may be due to the generation of high levels of B memory cells and their steady recruitment to form antibody secreting cells. Some diseases, notably AIDS, are a much greater challenge and it will need all the expertise of molecular biologists and immunologists to devise a vaccine which may control the disease. Vaccination to enhance or decrease the action of hormones is now being actively explored as a practical way of controlling fertility in mammals or enhancing selected properties of other hormones. In this situation, the desired effect is for a defined period, possibly one year or less. These requirements underline further the need for controlled release formulations for vaccine delivery.