Adjuvancy

How do adjuvants increase vaccine efficacy?

An adjuvant is a substance which is added to a vaccine to increase its efficiency. The word adjuvant has its origin from the Latin “adjuvare” which means “to help”. From a chemical point of view, adjuvants are a highly heterogenous group of compounds that share only one functional characteristic: that of being able to enhance immune responses. Adjuvants improve the presentation of antigens, resulting in a stronger immune response and the production of memory cells.  

There are still challenges with existing vaccines regarding providing sufficient immunogenicity; adjuvants can help with this as well as antigen sparing. The improved immune response in the presence of an adjuvant means less antigen is required in the formulation. This has many benefits, including:

• Reducing adverse reactions at the injection site without impacting the strength of the immune response
• Requiring fewer injections of the vaccine
• Decreasing formulation cost and speeding up vaccine production 

Although adjuvants can be classified according to the type of immunity they best stimulate, this becomes problematic because most adjuvants activate both humoral and cell-mediated immunity. Only the extent of stimulation varies with different adjuvants. Furthermore, the antigen with which the adjuvant is mixed may also influence the outcome of the immunisation. Finally, adjuvants can be classified according to the Toll-like receptors they may interact with. 

The most commonly used adjuvants are: mineral-based adjuvants (aluminium hydroxides and aluminium phosphates), oil emulsions and purified extracts from the Quillaja Saponaria Molina tree. Croda has manufactured adjuvants for human and veterinary vaccines since 1939 and is the only company to manufacture sterile mineral-based adjuvants using an aseptic process.

Immunisation in developing countries 

There are long geographical distances between the vaccinating physician and the population. Valuable resources can be saved if protection can be achieved using two injections instead of three. Precision vaccines targeted at vulnerable populations are also of increasing importance.