Like lead, aluminium is a highly neurotoxic metal. We will therefore expect vaccines containing aluminium adjuvants to cause neurological harms if the aluminium enters the nervous system in neurotoxic amounts. 

The aluminium in the adjuvant is important for eliciting a strong immune response in non-live vaccines and their efficacy is related to their toxicity at the injection site.1-3 Immune-reactive cells engulf particles of aluminium adjuvant and distribute their load throughout the body, including to the brain, where they are killed, releasing their contents into the surrounding brain tissue where they can produce an inflammatory response.

The precise mechanism of action is not so important, but the data we have on the harms are, and they have been systematically distorted.