The Truth about Thimerosal

The use of thimerosal in vaccines has been under scrutiny by the general public and by medical organizations throughout the United States for many years. Thimerosal is a vaccine additive that prevents germs from growing inside them, which prevents the potential consequences of illness and death. Those who oppose the utilization of thimerosal in vaccines feel that there is too much mercury in the compound for it to possibly be safe enough for use in children. However, it has been all but proven throughout years of countless journal publications and studies conducted by medical professionals, that thimerosal is safe to use in vaccinations for children. These statements lead to two reasonable questions: why are people still skeptical of the safety of thimerosal if it has been proven to be safe, and if it has been proven to be safe, why is it no longer used in children’s shots?

The chemical structure of thimerosal is shown here.

To answer these questions, we’d have to flash back to 1997, when the FDA (U.S. Food and Drug Association) Modernization Act was implemented. Part of this bill was an amendment, which gave the FDA two years to “compile a list of drugs and foods that contain intentionally introduced mercury compounds and [to] provide a quantitative and qualitative analysis of the mercury compounds on the list.” What the FDA found regarding the use of mercury compounds in vaccines was that infants could receive as much as 187.5 micrograms of mercury by the time they reached six months of age. In order to gauge whether or not the amount of mercury in vaccines was safe or not, the FDA examined safety guidelines from their own agency, and from the Environmental Protection Agency and the Agency for Toxic Substances and Disease Registry. While they did find guidelines for methylmercury (environmental mercury), they did not find any for ethylmercury (thimerosal). Since ethylmercury is significantly less likely to accumulate in the body, the FDA decided that the guidelines for methylmercury were not necessarily predictive of the safety of thimerosal.

The FDA shared their findings with the CDC (Centers for Disease Control and Prevention) and the AAP (American Academy of Pediatrics), both of which are organizations that are responsible for making vaccine recommendations for U.S. children. There was a slight concern by several parties involved that there were no studies that compared neurological outcomes in children who had received vaccines containing thimerosal with those who had not. As a precaution, the CDC and AAP asked pharmaceutical companies to remove thimerosal from vaccines. Following this decision, the AAP issued a press release which stated that “parents should not worry about the safety of vaccines” and that “the current levels of thimerosal will not hurt children, but reducing those levels will make safe vaccines even safer.” As could be expected, critics were skeptical of the claim that removing an allegedly safe compound from a vaccine could make it any safer.

This skepticism ignited a wave of anti-vax sentiment among parents especially, who became frightened at the sudden change in policy, and reasoned that because of it, thimerosal must be harmful. In this case, the precautionary principle failed the CDC/AAP, who were simply seeking to maximize the safety of vaccines, but ended up causing a panic among the general public regarding the safety of thimerosal, which has actually been harmful in the long run due to its long-term contribution to vaccine hesitancy. There are still individuals today who feel that vaccines are unsafe due to thimerosal, when the compound is not even used in vaccines anymore (other than certain variants of the influenza vaccine). Advocacy groups have originated among parents based on the belief that thimerosal-containing vaccines caused their children’s autism.

This humorous comic pokes fun at the hypocrisy of those anti-vax parents who are vehemently against the use of vaccines, but are open to the idea of injecting mercury-chelating agents into their children as an attempt to cure their autism (one child has even died as a result from the mercury-chelating agent EDTA).

Since 1999, it has been proven through extensive studies that there is no link between thimerosal and autism (or any other kind of neuropsychological condition). Thimerosal has been used to prevent bacterial contamination since the 1930s, so any rise in the diagnosis of autism throughout the years could not possibly be due to the compound anyways. Furthermore, it has been determined that the kind of mercury in thimerosal (ethylmercury) does not stay in the body long enough to cause illness. While certain side effects can be attributed to the use of thimerosal in vaccines, they are very minor (localized redness and swelling at the site of injection) and extremely short lived (1-2 days). However, since the backlash of the reintroduction of a vaccine component that is deemed dangerous by many and is not absolutely necessary for the vaccine’s function would be severe and potentially harmful for the reputation of vaccines in general, thimerosal remains a removed ingredient.

The legacy of thimerosal is indicative of how the actions of medical organizations (even those that are solely precautionary in nature) can strike fear into the hearts of the general public. The only way to combat this source of vaccine hesitancy is to educate those unaware of what thimerosal is actually made of, and why it is safe for use in vaccines. Unfortunately, anti-vax sentiment has reached a point where there are many whose minds on the subject will never waver, but that does not mean that all is lost. If public schools (high schools and/or middle schools) across the nation were to implement an introductory course on vaccines and how they work, the generations to come could have a better understanding of vaccinations in general, and prevent outbreaks of diseases for which vaccines are available, like the ones that have been occurring in recent years.

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