Description of the intervention
Adjuvants are added to vaccines to enhance the ability to provoke an immune response of weak antigens and improve the overall potency of the vaccine (O’Hagan 2009; Coffman 2010). Adjuvants may also pose other benefits, such as reducing the frequency of vaccination and the dose of antigen per vaccine, and some may provide cross-clade immunity (i.e. immunity against different clades of viruses or different clades of bacteria descending from different ancestors) or improve the stability of the final vaccine formu-lation (Carter 2010; Reed 2013). Currently, five adjuvants with completely different mechanism of action are approved for use in vaccine production.