Sarah Bennett
Thimerosal, a preservative containing ethylmercury, has been a cause for concern for parents and health authorities alike. While the FDA has maintained that there is no evidence of harm caused by thimerosal, the Public Health Service, including the FDA, CDC, and American Academy of Pediatrics, recommended reducing childhood exposure to mercury from all sources, including vaccines, as a precautionary measure in 1999. This led to the removal of thimerosal from vaccines routinely given to infants, and now, vaccines recommended for children under six years in the US no longer contain thimerosal as a preservative. However, some influenza vaccines still contain thimerosal, and parents in California continue to express concern about the presence of thimerosal in vaccines for infants.
| Characteristics | Values |
|---|---|
| Thimerosal content in vaccines | Since 2001, thimerosal has been removed from all routine childhood vaccinations in the U.S. Some influenza vaccines still contain thimerosal. |
| Thimerosal and neurodevelopmental disorders | Several valid scientific studies have shown there is no link between thimerosal and neurodevelopmental disorders, including autism. |
| Thimerosal and mercury exposure | Thimerosal is approximately 50% mercury by weight. Depending on the vaccine formulations used and the weight of the infant, some infants may be exposed to cumulative levels of mercury during the first six months of life that exceed Environmental Protection Agency (EPA) recommended guidelines for safe intake of methylmercury. |
| Thimerosal and allergic responses | Other than allergic responses in some individuals, there was no known health risk from thimerosal-preservative at the concentration used in vaccines. |
| Thimerosal and vaccine safety | All vaccine ingredients undergo rigorous scientific testing to ensure their safety. The FDA has actively addressed the issue of thimerosal as a preservative in vaccines, and its use has significantly declined due to reformulation and the development of single-dose containers. |
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What You'll Learn
- Thimerosal is no longer used in routine childhood vaccinations in the US
- There is no evidence linking thimerosal to autism or other neurodevelopmental disorders
- The FDA has reviewed thimerosal use in childhood vaccines and found no evidence of harm
- Some influenza vaccines still contain thimerosal as a preservative
- The use of thimerosal in vaccines is declining due to reformulation and single-dose containers
Thimerosal is no longer used in routine childhood vaccinations in the US
Thimerosal, also known as thiomersal, is an organic compound containing mercury, also known as ethylmercury. It is used as a preservative in vaccines to prevent bacterial and fungal contamination. Since the 1930s, it has been widely used as a preservative in a number of biological and pharmaceutical products, including many vaccines, to prevent the growth of harmful microbes inadvertently introduced into the vaccine during use.
In 1999, the FDA reviewed the use of thimerosal in childhood vaccines and found no evidence of harm from the use of thimerosal as a preservative, other than hypersensitivity reactions. However, the review also evaluated the amount of mercury an infant might receive from vaccines under the US-recommended childhood immunization schedule. It was found that some infants could be exposed to cumulative levels of mercury during the first six months of life that exceeded the Environmental Protection Agency's (EPA) recommended guidelines for safe intake of methylmercury.
As a result, in 1999, the FDA, along with the Public Health Service, the National Institutes of Health (NIH), the CDC, the Health Resources and Services Administration (HRSA), the American Academy of Pediatrics (AAP), and the American Academy of Family Physicians (AAFP) concluded that, as a precautionary measure, it was prudent to reduce childhood exposure to mercury from all sources, including vaccines, as much as possible. Subsequently, the FDA sent a letter to all manufacturers of US-licensed vaccines, requesting their plans to remove thimerosal from their vaccines.
Following this, thimerosal was removed from childhood vaccines in the US by 2001. Today, all vaccines routinely recommended for children 6 years of age and younger in the US are available in formulations that do not contain thimerosal. However, influenza (flu) vaccines are currently available in both thimerosal-containing (for multi-dose vaccine vials) and thimerosal-free versions.
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There is no evidence linking thimerosal to autism or other neurodevelopmental disorders
Thimerosal is an organic mercury compound that has been used as a preservative in some vaccines since the 1930s. It is used to prevent bacterial and fungal contamination, which can lead to serious illness and even death. While thimerosal is approximately 50% mercury by weight, it is important to note that ethylmercury, the metabolite of thimerosal, has a significantly shorter half-life than methylmercury. This distinction is crucial when considering the potential health risks associated with thimerosal exposure.
Despite concerns about the potential link between thimerosal-containing vaccines and autism or other neurodevelopmental disorders, extensive research has failed to find any evidence to support this hypothesis. The Immunization Safety Review Committee of the Institute of Medicine rejected the idea of a causal relationship between thimerosal-containing vaccines and autism in 2004. Multiple epidemiologic studies and pharmacokinetic studies have also been unable to establish a cause-and-effect connection.
In 1999, the American Academy of Pediatrics and the US Public Health Service issued a joint statement recommending the removal of thimerosal from vaccines as a precautionary measure. This decision was made due to scientific uncertainty at the time and the potential risk of mercury exposure from all sources, including vaccines. However, it is important to note that even after thimerosal was removed from almost all childhood vaccines, autism rates continued to rise. This observation contradicts the theory that thimerosal causes autism.
A retrospective cohort study conducted in the UK investigated the association between thimerosal-containing vaccines and neurodevelopmental disorders in a large cohort of over 100,000 subjects. The researchers assessed the receipt of DTP or DT doses and cumulative exposure to thimerosal by 6 months. While 96% of the term infants assessed received all 3 doses, only 0.1% of the neurodevelopmental diagnoses were autism. This study provides further evidence against a significant association between thimerosal exposure and autism.
In summary, while there have been concerns about the potential link between thimerosal-containing vaccines and autism or other neurodevelopmental disorders, the available scientific evidence does not support this hypothesis. The removal of thimerosal from vaccines was a precautionary measure, and the increase in autism rates despite the reduction of thimerosal in vaccines further weakens the argument for a causal relationship. As such, it is safe to conclude that there is no evidence linking thimerosal to autism or other neurodevelopmental disorders.
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The FDA has reviewed thimerosal use in childhood vaccines and found no evidence of harm
Thimerosal is a mercury-containing compound that has been used as a preservative in vaccines since the 1930s. It is used to prevent the growth of harmful microbes inadvertently introduced into the vaccine during use. The use of thimerosal in vaccines has been a topic of concern for many parents and researchers, with some studies estimating that infants could have been exposed to cumulative levels of mercury during the first six months of life that exceeded Environmental Protection Agency (EPA) guidelines for safe intake.
In response to these concerns, the FDA has conducted multiple reviews of thimerosal use in childhood vaccines. Under the FDA Modernization Act (FDAMA) of 1997, the FDA conducted a comprehensive review of thimerosal in 1999, evaluating the amount of mercury an infant might receive under the recommended childhood immunization schedule. This review found no evidence of harm from the use of thimerosal as a preservative, other than local hypersensitivity reactions.
However, due to scientific uncertainty at the time, the FDA, along with other health organizations, recommended reducing childhood exposure to mercury from all sources, including vaccines, as a precautionary measure. As a result, the use of thimerosal as a preservative in FDA-approved vaccines has significantly declined, and vaccine manufacturers have worked to produce thimerosal-free formulations or reduce the amount of thimerosal in vaccines.
Since the initial review in 1999, the FDA has continued to monitor the safety of thimerosal in vaccines. Multiple studies and risk assessments have been conducted, and the FDA has consistently found no evidence of harm from the use of thimerosal in childhood vaccines. These findings have been supported by other organizations, such as the Centers for Disease Control and Prevention (CDC) and the Institute of Medicine (now known as the National Academy of Medicine).
While thimerosal has been removed from most childhood vaccines in the United States, it is still used in some flu vaccines. However, thimerosal-free versions of these vaccines are available, and the CDC states that they are working with manufacturers to reduce or replace thimerosal in vaccines as soon as possible.
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Some influenza vaccines still contain thimerosal as a preservative
Thimerosal is a mercury-based preservative that has been used in vaccines since the 1930s. It is approximately 50% mercury by weight, and its use as a preservative in vaccines has been declining due to the reformulation and development of single-dose vaccines.
In 1999, the Public Health Service, the FDA, the NIH, the CDC, the HRSA, the American Academy of Pediatrics, and the American Academy of Family Physicians agreed that thimerosal should be reduced or removed from vaccines as a precautionary measure. This was due to concerns that infants could be exposed to cumulative levels of mercury during the first six months of life that exceeded EPA guidelines for safe intake of methylmercury.
However, it is important to note that research has not found any evidence of harm from the use of thimerosal as a preservative in vaccines, except for local hypersensitivity reactions and redness and swelling at the injection site. Multiple studies have also found no link between thimerosal in vaccines and autism or other neurodevelopmental disorders.
Today, thimerosal is still used as a preservative in some influenza vaccines, specifically those in multi-dose vials, to prevent contamination by germs, bacteria, and fungi. Single-dose vaccines, on the other hand, do not typically contain thimerosal. The CDC's ACIP does not preferentially recommend vaccines that do not contain thimerosal for any populations, and states that the benefits of flu vaccination outweigh any risk from thimerosal exposure.
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The use of thimerosal in vaccines is declining due to reformulation and single-dose containers
Thimerosal is a mercury-based preservative that has been used for decades in the United States in multi-dose vials of vaccines and medicines. It is added to vials containing more than one dose to prevent the growth of harmful microbes, such as bacteria and fungi, which can be introduced when a syringe needle enters a vial during vaccine preparation.
Despite its documented antimicrobial properties, concerns have been raised about the safety of thimerosal due to its mercury content. In response, the use of thimerosal in vaccines has declined significantly due to reformulation and the development of single-dose containers.
In 1999, the American Academy of Pediatrics and the U.S. Public Health Service recommended removing thimerosal from vaccines as a precautionary measure. This led to manufacturers working with the FDA to produce thimerosal-free or reduced formulations, particularly for childhood vaccines. By 2001, thimerosal had been removed from most childhood vaccines, with the exception of certain inactivated influenza vaccines.
Today, thimerosal is rarely used in vaccines in the U.S., and single-dose influenza vaccines without thimerosal are now standard. The decline in thimerosal use is also attributed to the development of new products formulated into single-dose presentations that do not require preservatives.
While there is no scientific evidence of harm from thimerosal at the concentrations used in vaccines, the precautionary measures reflect the principle of minimizing childhood exposure to mercury from all sources.
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Frequently asked questions
Thimerosal has been removed from all routine childhood vaccinations in the U.S. since 2001. However, some influenza vaccines still contain thimerosal.
Thimerosal is a preservative that contains ethylmercury. While there is no evidence of harm from the use of thimerosal as a vaccine preservative, the FDA recommended removing it from vaccines routinely given to infants as a precautionary measure.
Research does not show any link between thimerosal in vaccines and autism. Many well-conducted studies have concluded that thimerosal does not contribute to the development of autism.
