Some vaccines contain or have contained thimerosal, a mercury-based preservative, although its use has significantly declined and is mostly absent from vaccines routinely given to young children.
True
There’s mercury based ingredients in vaccines.
Thimerosal and Vaccines
Source: nfid.org
At a glance
Verified August 2, 2025Key Evidence
The FDA and CDC confirm that thimerosal is a mercury-containing organic compound used as a preservative in some vaccines, primarily multi-dose vials.
Its use has declined significantly, especially in vaccines for young children, with no evidence of harm from the low doses present.
fda.govfda.govThimerosal and Vaccines
cdc.govcdc.govThimerosal and Vaccines
Thimerosal contains ethylmercury, which differs from more toxic forms of mercury and is cleared quickly from the body.
npr.orgnpr.org4 things to know about the vaccine ingredient thimerosal
The reporting
What the Evidence Shows
Thimerosal is an organomercury compound that has been used as a preservative in multi-dose vaccine vials to prevent bacterial and fungal contamination. It contains ethylmercury, a form of mercury that is processed and cleared from the body more rapidly than methylmercury, the type found in fish. While thimerosal was commonly used in vaccines for decades, its use has markedly declined due to reformulation efforts and the development of single-dose vaccine presentations.
Since 2001, most vaccines routinely recommended for children under six years of age in the United States are thimerosal-free, except for some formulations of the inactivated influenza vaccine. There is no credible scientific evidence that the low doses of thimerosal used in vaccines cause harm beyond minor local reactions.
Therefore, the claim that vaccines contain mercury-based ingredients is accurate but requires context regarding the type of mercury compound involved and its current limited use.
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