Which metal is found in some vaccines?

• A. Mercury
• B. Lead
• C. Arsenic
• D. Cadmium

Answer: (A)

Mercury can be present in vaccines in the form of thimerosal, a preservative used historically to prevent contamination in multi-dose vials. Thimerosal contains ethylmercury, a mercury compound; the amounts used are very small, and health authorities have deemed them safe in vaccines when needed. In contrast, lead, arsenic, and cadmium are toxic metals not used as ingredients in vaccines, so they wouldn’t be included. Some vaccines today are formulated without thimerosal, especially for children, though a few multi-dose influenza vaccines in certain settings may still use it. The key point is that mercury is the metal associated with some vaccines through thimerosal, whereas the other metals listed are not part of standard vaccine formulations.