evidence: Aluminum-containing vaccines are generally injected into the muscle, and the aluminum is released gradually into the bloodstream from the injection site over time. Taking into account the multiple possible sources of aluminum in the babies’ blood and the slow release from the vaccines, the body burden of aluminum would not be expected to rise above the safe limit, the researchers found. In fact, the level stayed at less than half the safe limit, they wrote, pointing out that this limit itself has a cushion built in and that exposure at or slightly above the limit might be safe. "We conclude that episodic exposures to vaccines that contain aluminum adjuvant continue to be extremely low risk to infants and that the benefits of using vaccines containing aluminum adjuvant outweigh any theoretical concerns," the FDA researchers wrote. The researchers found that during infancy, the aluminum from vaccines at most might contribute twice the amount that the body absorbs from dietary sources, taking into account that the vast majority of aluminum in food or drinks is never absorbed into the body. Other research has indicated that overall, vaccines contribute a negligible amount of aluminum to children’s total exposure.