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PAUL A. OFFIT, MD: An adjuvant is something added to a vaccine to enhance the immune response so that one can give either lesser quantities of the vaccine or fewer doses of the vaccine. The only adjuvant that we're currently using in the United States is aluminum salts.

MARK SAWYER, MD: But what you need to know is that aluminum is in our environment everywhere in the world: aluminum cans, formula that we feed babies has aluminum in it; even breast milk has aluminum in it. So the amount of aluminum that you're exposed to through vaccines is extremely small compared to the amount that we face every day in our daily life.