Programs for vaccination against the new influenza A/H1N1 targeting many hundred million citizens in Europe and the USA are to be launched in the fall of this year. The USA is planning to employ a non-adjuvanted vaccine, whereas European nations are opting for inclusion of MF9, the adjuvant contained in an alternative seasonal flu vaccine, or the related adjuvant AS03 that is contained in a recentlyeveloped H5N1 vaccine.
We draw attention to unappreciated hazards of using adjuvanted vaccine in Europe. Evidence from animal experiments in conjunction with clinical epidemiological data indicates that, quite irrespective of cause, stimulation of the immune system may accelerate atherogenesis.
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Atherosclerosis is a case in point. Mobilization of innate immune components to intimal lipids possibly represents a physiological means to clear tissues of cholesterol, whose poor solubility necessitates its removal by macrophages. Clinical manifestations of atherosclerotic vessel disease ensue only when pathological late lesions evolve as the cholesterol removal machinery breaks down through overload. Lesional macrophages then cease to execute their physiological function in a quiescent manner and detrimental effects follow with all the known clinical consequences.
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Atherogenesis: The process of forming atheromas, plaques in the inner lining (the intima) of arteries. Strokes, heart attack or even death can be caused by the buildup of plaque in the arteries. The plaque itself is a result of cholesterol problems, smoking, and high blood pressure. 
Invoking a robust inate immune response using an adjuvent can potentially over-stimulate the macrophages that are attempting to clear the fatty tissue. This leads to inflamation of the macrophages, and ultimatly heart attack or stroke.
Application of adjuvanted flu vaccines to individuals at risk may therefore aggravate the course of underlying atherosclerotic vessel disease with all the clinical consequences. The same may hold true for other widespread diseases that are propelled by deregulated immune mechanisms.
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Safety trials conducted to date have not specifically taken these possible side effects into account, and unexpected serious adverse effects thus may follow in the wake of a general vaccination program.
If, at any stage, vaccination drives macrophages into their inflammatory state, the effects on atherosclerosis will hardly be unpredictable and acute clinical events could be precipitated. Causes might be the adjuvant or another ingredient, a combination of both, or any other inflammatory events provoked by intramuscular injection of the vaccine.
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Sucharit Bhakdi - Institute of Medical Microbiology and Hygiene
Karl Lackner - Department of Clinical Chemistry and Laboratory Medicine
Hans-Wilhelm Doerr - Department of Medical Virology
Published online: 23 October 2009
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