Definition: The adjuvant is the component of a vaccine that stimulates the immune system to react against the pathogen represented by the vaccine's other components.
The most important components of a vaccine are the antigen and the adjuvant. The antigen, usually a piece of protein from a bacteria or virus, tells the immune system what to react to, and the adjuvant tells it to react. The choice of adjuvant can make an enormous difference in how effectively a vaccine stimulates an immune response.
Examples:
Cervarix, an HPV vaccine approved in the United States in October of 2009, is the first vaccine containing the adjuvant monophosphoryl lipid A (MPL) to be licensed by the FDA.
