Squalene is a 30-carbon branched structure made from isoprene units in the production of cholesterol and other endogenous compounds such as glucocorticoids and sex steroids.
We all have squalene in our bodies. We NEED squalene. All mammals make squalene. Even fungi make squalene (for a compound called ergosterol that is required in their cell membranes).
So ubiquitous is squalene is that it is extracted commercially from shark liver oil. Squalene is intentionally added to cosmetics sold as “natural.”
Squalene is also a component of a vaccine adjuvant that has been used for over 10 years in Europe but is still pending approval in the US for use in the H1N1 flu vaccine.
In the context of immunology, an adjuvant is a chemical or combination of chemicals used to improve the immune response to vaccines.
But squalene is already in our bodies. We make the stuff. A vaccine with squalene will just be adding a little more squalene into our bodies.