evidence: Some people concerned about vaccine safety wonder whether vaccines may enter the brain and cause neurological conditions. In order to affect the brain, vaccine components would need to reach the brain. Importantly, our brains are protected by a barrier, called the blood-brain barrier (BBB), which keeps foreign substances from entering the brain. [...] - Aluminum salts -Many vaccines contain aluminum salts to boost the response to the vaccine. When aluminum salts enter the bloodstream, most are bound by a protein, called transferrin, and filtered out of the body by the kidneys. While more than half of the quantity of aluminum that enters the body is removed within 24 hours of injection, and 75% within two weeks, small amounts of aluminum, introduced either through vaccination or through the diet, may remain in the body. Most of this aluminum accumulates in the bones, but about 1% of residual aluminum is estimated to accumulate in the brain. Most often, health issues that involve aluminum are experienced by people whose kidneys are not working well or not working at all AND who have been exposed to high levels of aluminum over a long period of time. In these situations, health issues could be associated with the bones or brain. However, the role of aluminum in brain-based diseases remains uncertain. [...] If you are concerned that your child is suffering from meningitis or encephalitis, contact your healthcare provider immediately.