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Which flu vaccines contain squalene-based adjuvants and who should or should not receive them?
Executive summary
Two widely discussed squalene-containing adjuvants used with influenza vaccines are MF59 and AS03; MF59 is the adjuvant in Fluad, an FDA‑licensed vaccine for adults ≥65, while AS03 and AF03 are other squalene-based oil‑in‑water adjuvants registered in various countries and in pandemic formulations [1] [2] [3]. Public health guidance generally recommends adjuvanted influenza vaccine (Fluad/MF59) as one acceptable option for older adults because it increases immune responses, but trials show somewhat higher local reactogenicity and clinical comparisons with other enhanced vaccines vary [4] [5] [6].
1. What “squalene” adjuvants are and which vaccines use them
Squalene is a naturally occurring triterpene oil used to make oil‑in‑water emulsion adjuvants that boost immune responses; the principal squalene‑based adjuvants reported in the influenza literature are MF59, AS03, and AF03 [2] [3]. MF59 is an oil‑in‑water emulsion containing squalene, polysorbate 80 and sorbitan trioleate and is the adjuvant in Fluad (used in seasonal vaccines for older adults) [3] [1]. AS03, developed by GSK, contains squalene plus DL‑α‑tocopherol and polysorbate 80 and has been used in pandemic and some licensed influenza formulations outside the U.S.; AF03 is another squalene‑containing oil‑in‑water adjuvant described in manufacturer materials [3] [2].
2. Which marketed influenza vaccines contain squalene
In the United States and in many clinical summaries, Fluad is repeatedly identified as the licensed seasonal influenza vaccine that contains the MF59 squalene emulsion and is approved for people aged 65 and older [1] [4] [5]. Medical reviews and vaccine‑choice guides list Fluad/MF59 as the adjuvanted option among “enhanced” vaccines for seniors—alongside high‑dose and recombinant formulations—recommended by advisory committees for older adults [4] [5].
3. Who public health bodies and experts say should receive them
Advisory guidance cited in the reviewed material recommends that adults ≥65 should receive an enhanced influenza vaccine; acceptable options include an MF59‑adjuvanted vaccine (Fluad), a high‑dose vaccine, or a recombinant HA vaccine—meaning older adults are a primary target group for squalene‑adjuvanted seasonal flu vaccines [4] [5]. For certain immunocompromised groups, some authorities state that inactivated and recombinant vaccines are generally acceptable and that adjuvanted or high‑dose vaccines may be considered for solid‑organ transplant recipients aged 18–64 on immunosuppression [4] [5].
4. Safety, reactogenicity, and dispute context
Clinical trials and reviews show MF59‑adjuvanted vaccines produce stronger antibody responses in older adults and can reduce symptomatic illness or hospitalizations in some studies, but they also have higher rates of local reactions (pain, tenderness, induration) and some analyses found no clear superiority in certain elderly subgroups with chronic conditions [4] [5] [6]. Several reviews conclude squalene is poorly immunogenic and that concerns about anti‑squalene antibodies or systemic harms are not supported by the clinical evidence summarized in those papers [7] [8]. However, older meta‑analyses and some investigators found limited or mixed evidence on clinical outcome superiority for MF59 in certain populations, so benefits versus alternatives remain debated in parts of the literature [6].
5. Mechanism and practical implications for vaccine choice
Squalene‑based emulsions act by engaging innate immunity, recruiting antigen‑presenting cells and improving antigen uptake; this increases magnitude and breadth of hemagglutinin‑specific B‑cell and antibody responses, which can widen protection across virus variants and allow antigen dose‑sparing in production [2]. Practically, choice of vaccine for older adults often balances greater immunogenicity (and some evidence of fewer hospitalizations) with somewhat increased local side effects; public health bodies therefore list adjuvanted vaccines as one of several valid enhanced options [4] [5].
6. Gaps, disagreements, and what reporting does not say
Available sources do not list every brand‑name influenza product worldwide that has used AS03 or AF03 in specific seasons; instead the literature notes MF59 (Fluad) as the primary seasonal adjuvanted product in many countries and AS03/AF03 as other registered squalene‑based adjuvants used in pandemic or some regional vaccines [3] [2]. Some older reviews found no clear mortality benefit over other vaccines in certain elderly subgroups and flagged increased local reactions, indicating that evidence on clinical superiority is not unanimous [6]. Where sources explicitly address safety concerns about squalene‑associated antibodies, they report no meaningful elevation in anti‑squalene antibodies after vaccination [7] [8].
If you want, I can list—by country or by year—specific influenza products that used AS03 or AF03 in pandemic or seasonal programs, using only the sources you provide.