Characterization of aluminium-containing adjuvants

The approved aluminium-containing vaccine adjuvants have been shown to be poorly crystalline aluminium oxyhydroxide (AIO(OH)) and amorphous aluminium hydroxyphosphate of varying phosphate content. Adsorption of the antigen by the adjuvant is implied in many proposed mechanisms of antibody production enhancement caused by the adjuvants. The World Health Organization recommends adsorption of 80% or more of tetanus and diphtheria toxoid by the aluminium-containing adjuvants. Thus, one objective in the preparation of vaccines containing these adjuvants is to optimize adsorption of the antigen on the adjuvant. Production of a consistent adjuvant effect in vaccines would be facilitated by the thorough characterization of aluminium-containing adjuvants with reference to properties that affect adsorption and other colloidal behaviour. Such properties include surface area, surface charge, chemical composition, structure, and morphology. Techniques and measurements such as X-ray diffraction, infrared spectroscopy, transmission electron microscopy, energy-dispersive spectrometry, Doppler electrophoretic light scattering analysis, dissolution rates, and adsorption isotherms provide a basis for understanding and predicting interactions and behaviour in monovalent as well as multivalent vaccines. Such characterization would be crucial in vaccine standardization and quality control.