Sarah Bennett
Thimerosal, a mercury-based preservative, has been used in multi-dose vials of vaccines and medicines in the United States for decades. While it has been phased out of most vaccines, it is still used in multi-dose vials of flu vaccines. Thimerosal has been a controversial topic due to concerns about potential links to autism and other neurodevelopmental disorders. However, extensive scientific research has found no credible evidence of a causal relationship between thimerosal-containing vaccines and autism or other developmental issues. This includes studies conducted on the MMR vaccine, which has never contained thimerosal.
| Characteristics | Values |
|---|---|
| Thimerosal content in MMR vaccine | Thimerosal is a mercury-based preservative added to multi-dose vials of vaccines to prevent bacterial and fungal contamination. Measles, mumps, and rubella (MMR) vaccines do not and never did contain thimerosal. |
| Thimerosal safety concerns | There is no evidence of harm caused by low doses of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site. Studies have found no association between thimerosal exposure and autism or other neurodevelopmental disorders. |
| Thimerosal reduction and removal | In 1999, health authorities recommended reducing or eliminating thimerosal in vaccines as a precautionary measure due to concerns over infant exposure to mercury. Thimerosal was removed from childhood vaccines in the US by 2001, except for some influenza vaccines. |
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What You'll Learn
- Thimerosal is a mercury-based preservative used in some vaccines
- MMR vaccines do not and never did contain thimerosal
- Thimerosal was removed from US-licensed vaccines in 1999
- There is no evidence that thimerosal causes autism or other neurodevelopmental disorders
- Ethylmercury and methylmercury are processed differently in the human body
Thimerosal is a mercury-based preservative used in some vaccines
Thimerosal is a mercury-based preservative that has been used safely in vaccines for decades to prevent microbial growth. It has been added to vaccines during the manufacturing process to prevent the growth of harmful microbes inadvertently introduced into the vaccine during use. Since the 1930s, it has been widely used as a preservative in a number of biological and drug products, including many vaccines.
Thimerosal is a compound that contains a form of mercury known as ethylmercury. Ethylmercury is different from methylmercury, the type of mercury found in certain fish, which can accumulate in the body and potentially cause harm at high levels. Ethylmercury is broken down and cleared from the body much more quickly than methylmercury, making it less likely to build up and cause health problems.
In the United States, thimerosal has been removed or reduced to trace amounts in all routinely recommended childhood vaccines, with the exception of some multi-dose vials of influenza (flu) vaccine. Measles, mumps, and rubella (MMR) vaccines do not and never did contain thimerosal. Varicella (chickenpox), inactivated polio (IPV), and pneumococcal conjugate vaccines have also never contained thimerosal.
The use of thimerosal as a preservative in vaccines has declined due to reformulation and the development of vaccines supplied in single-dose presentations. Multiple well-conducted scientific studies have found no evidence that thimerosal in vaccines causes harm, except for minor reactions like redness or swelling at the injection site. There is also no evidence of a link between thimerosal-containing vaccines and autism or autism spectrum disorder (ASD).
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MMR vaccines do not and never did contain thimerosal
Thimerosal is a mercury-based preservative that has been used for decades in the United States in multi-dose vials of medicines and vaccines. It is added to vials of vaccines that contain more than one dose to prevent the growth of harmful bacteria and fungi. The introduction of these microbes can occur when a syringe needle enters a vial as a vaccine is being prepared for administration. Contamination by germs in a vaccine could cause severe local reactions, serious illness, or even death.
However, MMR vaccines do not and never did contain thimerosal. Varicella (chickenpox), inactivated polio (IPV), pneumococcal conjugate vaccines, and MMR vaccines have also never contained thimerosal. Influenza (flu) vaccines are available in both thimerosal-containing and thimerosal-free versions.
In July 1999, the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure. This was due to concerns that some infants could have been exposed to cumulative levels of mercury during the first six months of life that exceeded Environmental Protection Agency (EPA) recommended guidelines for safe intake of methylmercury.
Since then, thimerosal has been the subject of numerous studies, and there is no evidence of harm caused by the low doses of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site. In fact, thimerosal has a long record of safe and effective use, and data from many studies show no evidence of harm caused by the low doses of thimerosal in vaccines. Furthermore, several studies have now proven that thimerosal in vaccines did not cause autism.
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Thimerosal was removed from US-licensed vaccines in 1999
Thimerosal is a mercury-based preservative that has been used for decades in multi-dose vials of medicines and vaccines in the United States. It is added to prevent the growth of harmful microbes, such as bacteria and fungi, which can inadvertently be introduced into the vaccine during use.
In 1999, concerns were raised about the potential risk of mercury in vaccines. The FDA determined that infants might be exposed to cumulative doses of ethylmercury that exceeded federal safety guidelines for ingestion of methylmercury. On July 1, 1999, the FDA sent a letter to all manufacturers of US-licensed vaccines, requesting their plans to remove thimerosal. This was a precautionary measure to reduce childhood exposure to mercury from all sources, including vaccines, due to scientific uncertainty at the time.
The Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers jointly agreed that thimerosal should be removed or reduced from vaccines as soon as possible. By 1999, thimerosal had already been eliminated from at least one formulation of each vaccine on the recommended childhood immunization schedule for children aged six years or younger.
The use of thimerosal as a preservative in US-licensed vaccines has significantly declined since then due to reformulation and the development of single-dose vaccines that do not require preservatives. Today, all vaccines routinely recommended for children aged six years and younger in the US are available without thimerosal.
It is important to note that studies have found no evidence of harm caused by the low doses of thimerosal used in vaccines, except for minor reactions like redness and swelling at the injection site.
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There is no evidence that thimerosal causes autism or other neurodevelopmental disorders
Thimerosal is a mercury-based preservative that has been used for decades in the United States in multi-dose vials of vaccines. It is added to prevent the growth of harmful bacteria and fungi, which can cause severe local reactions, serious illness, or even death.
Despite concerns, several studies have found no evidence that thimerosal causes autism or other neurodevelopmental disorders. For example, a 2003 study in Sweden and Denmark found that more children were diagnosed with autism after thimerosal was removed from vaccines. Additionally, a 2004 study in the UK and a 2010 study by the CDC also found no link between thimerosal and autism. The CDC has stated that there is "no data or evidence of any harm caused by the level of exposure that some children may have encountered" from vaccines.
The use of thimerosal in vaccines has declined due to reformulation and the development of single-dose presentations. Thimerosal was removed from childhood vaccines in the US in 2001, except for some influenza vaccines. However, yearly flu vaccines are recommended for all children, and thimerosal-free versions are available.
While thimerosal is generally considered safe, some people may experience mild side effects such as redness and swelling at the injection site. It is important to note that the controversy surrounding thimerosal has led to negative media attention and hesitancy towards vaccines, which can have public health consequences.
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Ethylmercury and methylmercury are processed differently in the human body
Thimerosal, a mercury-based preservative, has been used for decades in multi-dose vials of vaccines and medicines in the United States. It is added to prevent the growth of harmful microbes, which can inadvertently be introduced into the vaccine during administration and cause severe reactions, serious illness, or even death.
Thimerosal is approximately 50% mercury by weight and is metabolized or degraded into ethylmercury and thiosalicylate. Ethylmercury is an organomercurial and is chemically distinct from methylmercury, which is found in certain kinds of fish and shellfish.
Methylmercury is the form of mercury that people in the United States encounter most frequently. It is formed when mercury, a naturally occurring element, is released into the environment from volcanic activity, rock erosion, and human activities such as burning coal. Bacteria in the environment then convert this inorganic mercury into methylmercury, which bioaccumulates in fish, shellfish, animals, and humans. High exposure levels of methylmercury are toxic to humans and can cause nervous system damage, skin problems, and kidney toxicity.
In contrast, ethylmercury is broken down and excreted from the body much more rapidly than methylmercury. It does not accumulate in the body and is, therefore, less likely to cause harm. Studies have shown that thimerosal exposure in vaccines does not cause mercury poisoning or increase the risk of autism spectrum disorder (ASD).
In summary, ethylmercury and methylmercury are distinct compounds with different toxic effects and processing pathways in the human body. While methylmercury exposure through consumption of fish and shellfish is a concern, ethylmercury in vaccines has not been found to pose significant health risks.
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Frequently asked questions
No, the MMR vaccine has never contained mercury.
Thimerosal is a mercury-based preservative that has been used for decades in the United States in multi-dose vials of medicines and vaccines. It is used to prevent the growth of harmful microbes.
There is no evidence of harm caused by the low doses of Thimerosal in vaccines. Multiple studies have been conducted to investigate the safety of Thimerosal-containing vaccines, and they have supported its safety.
