Adjuvants--a classification and review of their modes of action.

Since early this century, various substances have been added to vaccines and certain formulations have been devised in an attempt to render vaccines more effective. Despite a plethora of options, only aluminium salts have gained acceptance as human vaccine adjuvants and even veterinary vaccines are largely dependent upon the use of aluminium salts. Currently, many new vaccines are under development and there is a desire to simplify vaccination schedules both by increasing the number of components per vaccine and decreasing the number of doses required for a vaccine course. New, more effective adjuvants will be required to achieve this.