Vaccination, squalene and anti-squalene antibodies: facts or fiction?

Squalene, a hydrocarbon obtained for commercial purposes primarily from shark liver oil and other botanic sources, is increasingly used as an immunologic adjuvant in several vaccines, including seasonal and the novel influenza A (H1N1) 2009 pandemic flu vaccines. Nearly a decade ago, squalene was supposed to be the experimental anthrax vaccine ingredient that caused the onset of Persian Gulf War syndrome in many veterans, since antibodies to squalene were detected in the blood of most patients affected by this syndrome. This evidence has raised a widespread concern about the safety of squalene containing adjuvants (especially MF59) of influenza vaccines. Nevertheless, further clinical evidence clearly suggested that squalene is poorly immunogenic, that low titres of antibodies to squalene can be also detected in sera from healthy individuals, and that neither the presence of anti-squalene antibodies nor their titre is significantly increased by immunization with vaccines containing squalene (or MF59) as an adjuvant. This review summarizes the current scientific evidence about the relationship between squalene, anti-squalene antibodies and vaccination.