Adjuvants enhances or helps the vaccines in boosting their immune response. Almost all vaccines currently licensed have adjuvants. Most commonly used and oldest adjuvant is Alum.
The article published in nature Journal in 2004 discusses the history of adjuvants, their mechanism of action and types of adjuvants.
The review article by Invivogen classifies the adjuvants as per their mechanism of action (Pattern recognition receptors).
Below are the embedded YouTube videos on adjuvants.
This video briefly describes the adjuvants mechanism of action. Focus on audio only.
This short video lecture discusses the Aluminum in vaccines especially its side effects.
This video lecture describes in detail about the new adjuvants currently under development.