Adjuvants are chemicals added to a vaccine to increase the response and stimulate the immune system to generate a large amount of antibodies. Adjuvant comes from the Latin word, adjuvare, which means support.

An adjuvant is “a substance which accelerates, prolongs and enhances the quality of a specific immune [meaning antibody] response when incorporated into a vaccine formulation.”

The evolution of the use of adjuvants began with the diphtheria vaccines.

At the turn of the century, diphtheria was a common filth disease. For example, between 1910 and 1919, nearly 1300 people died per year from diphtheria in NYC alone. Remember this was before the discovery and widespread use of antibiotics.

The swelling in the throat caused by the release of the diphtheria toxin from Corynebacterium diphtheriae could lead to obstruction and if severe, could lead to death.

By 1895, an anti-toxin was discovered that could neutralize the toxin released into circulation. An injection of anti-toxin – a dose of antibodies – was a treatment. While the injection of the anti-toxin could not reverse the effects of the toxin on the local throat tissue, it would neutralize the toxin in circulation, protecting the heart and other organs from being attacked.

Large scale production of anti-toxin /antibodies was made by injecting a dose of diphtheria into horses. Researchers found that when an irritant was injected along with diphtheria toxin, a very large number of antibodies would result that could be harvested. They needed a better “production method.”

Adjuvants heighten the inflammatory response caused by the vaccination. Early adjuvants used in vaccines included bread crumbs, agar, tapioca, starch, oil lecithin and saponin (tree sap).  The mechanism of action for most adjuvants is not understood.

Adjuvants are broadly separated into two classes based on their mechanisms of action: 1) vaccine delivery systems and 2) adjuvants that stimulate the immune response.

Vaccine delivery systems include particulates, including emulsions, microparticles, and liposomes. They target the antigen-presenting cells (APC). In contrast, adjuvants that stimulate the immune system are predominantly derived from pathogens (viruses and bacterial cell walls).