Does Mercury in Vaccines Cause Autism? 

Thimerosal is a preservative that has been used in some vaccines since the 1930s (CDC, retrieved June 2005). Thimerosal consists of 49% ethylmercury and some have suggested, partly because of the known effects of methylmercury (an environmental contaminant often found in fish) as a toxic substance, that thimerosal delivered in vaccines causes autism to develop in some children. Much is known about the effects of the more dangerous methylmercury. Massive systemic damage can occur through excessive methylmercury exposure. The Food and Drug Administration (EPA, retrieved June 2005) has advised pregnant women, nursing mothers, and young children limit their intake of certain types of fish, like tuna, that tend to contain high levels of methylmercury in order to prevent excessive methylmercury consumption.

The CDC’s Reports on Methylmercury and Autism

Much less is known about ethylmercury, however, the CDC reports that the cumulative exposure to ethylmercury that occurred when thimerosal was used as a preservative in vaccines was less than the FDA and World Health Organization recommended maximum safe exposure to methylmercury. However, the EPA’s more stringent guideline for methylmercury exposure was exceeded. Therefore, given the heightened concern over mercury exposure, the suggested link between thimerosal and autism, and technology that exists for eliminating ethylmercury from vaccines, thimerosal has been removed from all vaccines in the U.S. with the exception of certain flu vaccines. Research into this putative link to autism was, and still is, clearly warranted.

Learn the Facts about Mercury in Vaccines and Autism 

But is there evidence for thimerosal causing autism? The most definitive study to date was conducted by Danish researchers (Hviid et al., 2003). It looked at thousands of children who received either vaccines containing thimerosal or vaccines without this preservative and found that the rates of autism were identical in the two groups. If thimerosal was causing autism, a difference should have been found. Thimerosal had been removed from the vaccines of other developed countries such as Canada and Denmark prior to it being removed from vaccines in the U.S., however, no decrease in the prevalence of autism has been detected in these countries (NYTimes, retrieved 06/25/05). In 2003 the American Academy of Pediatrics, an organization that called for the removal of thimerosal from vaccines in July 1999, summarizes the evidence of harm from it as follows, “No scientific data link thimerosal used as a preservative in vaccines with any pediatric neurologic disorder, including autism. Despite this, the Centers for Disease Control and Prevention, American Academy of Pediatrics, National Institutes of Health, and US Public Health Service have continued to investigate this issue to put theoretic concerns about this mercury-containing compound to rest.” Learn more with NECC today. 


Updated: September 22, 2023