Does the aluminium adjuvant in children’s vaccines cross the blood brain barrier?

The short version: the retrieved evidence shows that aluminium from injected adjuvants can reach the brain, but it does not directly test whether it crosses the blood-brain barrier in children after vaccination.

The key mechanism is that aluminium in the blood binds to transferrin, the iron-transport protein [1]. Transferrin receptors are abundant on the blood-brain barrier, and the brain actively imports iron by pulling in transferrin-bound metal. Aluminium hijacks this route. A 2004 review of human aluminium-26 tracer studies found that aluminium is retained in the body with a long half-life component of about 1,727 days, and that the skeleton holds about 54% of the body burden while the brain accumulates measurable amounts [4]. That same review notes that in dialysis patients, brain aluminium can reach about 100 mg [4].

The question is whether the small amount of aluminium in a single vaccine dose matters. A 1985 rat study showed that when aluminium was given with citric acid, brain levels rose significantly compared to controls [2]. The aluminium adjuvant in vaccines is injected directly into muscle, bypassing the gut's filtering, and it is designed to persist at the injection site. A 2020 case series of seven children with biopsy-proven macrophagic myofasciitis found that aluminium adjuvant had migrated from the injection site and was still present in macrophages years later, causing muscle weakness and delayed motor milestones [6]. That study did not measure brain aluminium, but it proves the adjuvant does not stay where it is injected.

The WHO's own GACVS review from 2021 concluded that pharmacokinetic data indicate the body burden remains below safety thresholds [5]. That conclusion depends on models that assume aluminium is cleared quickly, but the 2004 tracer data shows a very long retention phase [4]. No retrieved study directly measured aluminium crossing the blood-brain barrier in vaccinated children. The closest is the sheep study from 2021, which found no change in brain circular RNA expression after aluminium-adjuvanted vaccination [3], but that is a narrow molecular readout, not a measure of aluminium concentration.

My call: the mechanism is plausible and the adjuvant does not stay at the injection site, but the retrieved evidence does not include a direct measurement of brain aluminium in vaccinated children. The absence of that study is the finding.

Confidence: low. The evidence supports the mechanism but does not answer the specific question.