Towards an understanding of the adjuvant action of aluminium

This Timeline article provides an overview of the discovery and proposed mechanisms of action of aluminium salts, the most widely used vaccine adjuvants. The recent progresses and outstanding controversies on how aluminium salts function as adjuvants are also discussed. The efficacy of vaccines depends on the presence of an adjuvant in conjunction with the antigen. Of these adjuvants, the ones that contain aluminium, which were first discovered empirically in 1926, are currently the most widely used. However, a detailed understanding of their mechanism of action has only started to be revealed. In this Timeline article, we briefly describe the initial discovery of aluminium adjuvants and discuss historically important advances. We also summarize recent progress in the field and discuss their implications and the remaining questions on how these adjuvants work.