Mercury in vaccines is present in the form of a compound called thimerosal, which is a mercury-based preservative used to prevent bacterial and fungal contamination in multi-dose vaccine vials. Thimerosal contains ethylmercury, which is different from the toxic methylmercury found in some fish. Ethylmercury is metabolized and cleared from the body much more quickly, making it less likely to cause harm. Thimerosal has been used safely for decades, mainly to prevent the growth of germs in multi-dose vials, thereby ensuring vaccine safety. Because of concerns about mercury exposure, thimerosal has been removed or reduced to trace amounts in most childhood vaccines in the United States since 1999, except for some multi-dose influenza vaccines. Studies have shown no evidence of harm from the low doses of thimerosal used in vaccines beyond minor injection site reactions. Thimerosal- containing vaccines allow for safer use of multi-dose vials by reducing the risk of contamination that could cause serious illness or death.
Why Mercury (Thimerosal) is Used in Vaccines
- To prevent bacterial and fungal contamination in multi-dose vaccine vials.
- Protects against potential severe local reactions or serious illness caused by contamination.
- Enables safer vaccine storage and administration in multi-dose formats.
Safety and Regulation
- Ethylmercury in thimerosal is processed and eliminated quickly by the body.
- Removed or minimized in most vaccines as a precaution, not due to evidence of harm.
- Flu vaccines sometimes still use thimerosal in multi-dose vials for preservation.
- No link has been found between thimerosal in vaccines and autism or neurological harm.
This use of mercury in vaccines is a safety measure for preserving vaccine sterility rather than a harmful ingredient.
