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Are there safety concerns with squalene in flu shots?
Executive summary
Squalene is an oil found naturally in people and is used as part of oil-in-water adjuvants (MF59, AS03) in some influenza vaccines to boost immune response; Fluad (MF59) is FDA‑licensed for people ≥65 and no safety concerns were identified in large trials cited at approval [1] [2]. Scientific reviews find low or no increase in anti‑squalene antibodies after vaccination and conclude licensed squalene‑adjuvanted influenza vaccines have an established safety profile in many countries [3] [1]. Some older reports and opinion pieces raised concerns linking squalene to autoimmune effects based on animal studies or Gulf War veteran findings, but later clinical evidence and regulatory reviews did not confirm a causal safety signal for licensed vaccines [4] [3] [5].
1. What is squalene and why is it in some flu shots?
Squalene is a naturally occurring organic oil produced by humans and other organisms; it is used in highly purified form as part of oil‑in‑water emulsion adjuvants (MF59, AS03) to enhance immune responses, improve antibody breadth, and allow dose‑sparing in influenza vaccines [1] [6]. Regulatory and clinical descriptions note that Fluad contains MF59 (a squalene emulsion) and AS03 used in certain H5N1 preparations contains squalene plus other oily compounds like vitamin E [6] [7].
2. What do large trials and regulators say about safety?
When the FDA approved Fluad, a large trial and post‑licensure data—including about 27,000 older adults evaluated—reported no safety concerns identified with that product, supporting its licensing for people ≥65 [2]. Reviews and peer‑reviewed summaries conclude that squalene‑based emulsion adjuvants are widely used, have an established safety profile, and are generally well tolerated in adults and children while increasing immunogenicity [1].
3. Where did safety concerns originate?
Concerns trace to two lines of evidence: detection of anti‑squalene antibodies in some Gulf War veterans with multisystem complaints, and animal studies suggesting autoimmune‑like effects after certain squalene exposures. Early commentary warned these findings raised questions about squalene‑containing adjuvants such as MF59 [4] [3]. The Wired piece reported FDA statements that, at least in 2009, “there is no squalene in any FDA‑approved vaccine in the US” for seasonal flu and H1N1 at that time—context that helped calm public fears then [5].
4. How did later clinical evidence address those concerns?
Subsequent clinical investigations and reviews found that low titers of anti‑squalene antibodies can be present in healthy people and that vaccination with squalene‑adjuvanted vaccines did not significantly increase anti‑squalene antibody titers or link to clear clinical autoimmune disease; the literature summary states further clinical evidence suggested squalene is poorly immunogenic and vaccination did not raise antibody levels significantly [3]. Broader reviews of squalene adjuvants state they have established safety profiles and are used globally [1].
5. Competing perspectives and remaining limitations
Some consumer‑oriented articles continue to highlight animal studies or selective reports suggesting potential autoimmune risk; for example, a wellness site cited animal findings that squalene injections “could trigger lupus‑like autoimmune symptoms” [8]. Scientific reviews counter that clinical trials and surveillance for licensed products have not borne out those risks and that regulatory approvals relied on large safety datasets [3] [2]. Available sources do not mention long‑term, large‑scale prospective studies specifically designed to detect every possible autoimmune outcome over decades after squalene‑adjuvanted seasonal influenza vaccination—so absolute long‑term certainty is not documented in these excerpts (not found in current reporting).
6. Practical takeaway for patients and clinicians
Health authorities and medical reviews support the use of squalene‑adjuvanted influenza vaccines where indicated (e.g., Fluad for older adults) because they increase immune responses and have not produced safety signals in the trials cited at approval [7] [2]. If you have specific autoimmune conditions or vaccine questions, discuss vaccine choice with your clinician; CDC, FDA and product literature outline which vaccines contain adjuvants and their recommended use [6] [7].
Sources cited in this piece: scientific reviews and regulatory summaries on squalene adjuvants and influenza vaccines [4] [5] [3] [1] [7] [6] [2] and consumer reporting noting continued concerns [8].