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Thimerosal Key Messages & Talking Points

What is thimerosal? Is it the same as mercury?

• Thimerosal is a mercury-containing organic compound and has been used for decades in the United States and other countries. It’s use as a preservative in a number of biological and drug products, including many vaccines, to help prevent potentially life threatening contamination with harmful microbes.

• Mercury is a metal found naturally in the environment and affects the human body differently than thimerosal.

What is the difference between ethylmercury and methylmercury? How are they different?

• When learning about thimerosal and mercury it is important to understand the difference between two different compounds that contain mercury: ethylmercury and methylmercury. They are totally different materials.

• Methylmercury is formed in the environment when mercury metal is present. If this material is found in the body, it is usually the result of eating some types of fish or other food. High amounts of methylmercury can harm the nervous system. This has been found in studies of some populations that have long-term exposure to methylmercury in foods at levels that are far higher than the U.S. population. In the United States, federal guidelines keep as much methylmercury as possible out of the environment and food, but over a lifetime, everyone is exposed to some methylmercury.

• Ethylmercury is formed when the body breaks down thimerosal. The body uses ethylmercury differently than methylmercury; ethylmercury is broken down and clears out of the blood more quickly. Low-level ethylmercury exposures from vaccines are very different from long-term methylmercury exposures, since the ethylmercury does not stay in the body.

Does thimerosal cause autism?

• No. Research does not show any link between thimerosal and autism.

Is thimerosal safe for people?

• Yes. Thimerosal has been used safely in vaccines for a long time (since the 1930s) and has a proven track record of being safe. A variety of scientists have been studying the use of vaccines that have thimerosal in them for many years. They haven’t found any actual evidence that thimerosal causes harm.

Why was thimerosal removed from vaccines given to children?

• Although no evidence suggests that there are safety concerns with thimerosal, vaccine manufacturers have stopped using it as a precautionary measure.

• In 1999, the Food and Drug Administration (FDA) was required by law to assess the amount of mercury in all the products the agency oversees, not just vaccines. The U.S. Public Health Service decided that as much mercury as possible should be removed from vaccines, and thimerosal was the only source of mercury in vaccines.

• The decision to remove it was a made as a precautionary measure to decrease overall exposure to mercury among young infants.

• Thimerosal was removed from childhood vaccines in 2001.

Why is thimerosal used in some vaccines?

• Because it prevents the growth of dangerous microbes, thimerosal is used as a preservative in multi-dose vials of flu vaccines, about a third of flu vaccine doses that are available.

• Each time a new needle is inserted into the multi-dose vial, it is possible for microbes to get into the vial.

• The preservative, thimerosal, prevents contamination in the multi-dose vial when individual doses are drawn from it. Receiving a vaccine contaminated with bacteria can be very dangerous.

• For two childhood vaccines, thimerosal is used to prevent the growth of microbes (bacteria and other environmental contaminants) during the manufacturing process.

• When thimerosal is used this way, it is removed later in the process.

• Only trace (very tiny) amounts remain.

• Today, the only childhood vaccines that have trace amounts of thimerosal are: one vaccine DTaP and one DTaP-Hib combination vaccine.

Do all flu vaccines contain thimerosal?

• No. Influenza (flu) vaccines are currently available in both thimerosal-containing and thimerosal-free versions. The total amount of flu vaccine without thimerosal as a preservative at times has been limited, but availability will increase as vaccine manufacturing capabilities are expanded. This year, about 2/3 of flu vaccine that is manufactured will be thimerosal-free.

Why is thimerosal still in some flu vaccines that children may receive?

• To produce enough flu vaccine for the entire country, some of it must be put into multi-dose vials. These vials have very tiny amounts of thimerosal as a preservative. This is necessary because each time an individual dose is drawn from a multi-dose vial with a new needle and syringe, there is the potential to contaminate the vial with harmful microbes (toxins). So, this preservative is needed to prevent contamination of the vial (as a safeguard) when individual doses are drawn from it, and keep the children safety who are receiving the flu shot from the multi-dose vial. Children can safely receive flu vaccine that contains thimerosal.

• Flu vaccine that does not contain thimerosal is available in single-dose vials or.

What keeps today’s childhood vaccines from becoming contaminated if they do not contain thimerosal as a preservative?

• The childhood vaccines that used to contain thimerosal as a preservative are now put into single-dose vials or syringes, so no preservative is needed. In the past, the vaccines were put into multi-dose vials, which could become contaminated when new needles were used to get vaccine out of the vial for each dose.

Was thimerosal used in all childhood vaccines?

• No. Some other vaccines, including the measles, mumps, and rubella vaccine (MMR), do not and did not ever contain thimerosal or any preservative. Varicella (chickenpox), inactivated polio (IPV), and pneumococcal conjugate vaccines have also never contained thimerosal.

How can I find out if thimerosal is in a vaccine?

• For a complete list of vaccines and their thimerosal content level, you may visit the . Additionally, you may ask your health care provider or pharmacist for a copy of the vaccine package insert. It lists ingredients in the vaccine and discusses any known adverse reactions.

How does thimerosal work in the body?

• Thimerosal contains “ethylmercury,” which is a completely different form of mercury than elemental mercury or methylmercury, which are found in the environment and some kinds of fish. Elemental mercury and methylmercury stay in the human body and at high levels can make people sick. But ethylmercury (that is found in thimerosal) does not stay in the body a long time and clears out of the blood quickly, so it does not build up and reach harmful levels. In fact, when thimerosal enters the human body, it breaks down to ethylmercury and thiosalicylate, which are easily eliminated.

What are the possible side-effects of thimerosal?

• Most people don’t have any side effects from thimerosal, but some people will have mild reactions like redness and swelling at the place where the shot was given, which only last 1 to 2 days. It’s very unlikely you will have an allergic reaction to thimerosal. Research shows that most people who are allergic to thimerosal will not have a reaction when thimerosal is injected under the skin (Wattanakrai, 2007; Heidary 2005).

• Anyone who believes they have been injured by a vaccine should contact the National Vaccine Injury Compensation Program.

Does thimerosal use in vaccines interfere with brain activity?

• The study, “Thimerosal Exposure in Early Life and Neuropsychological Outcomes 7-10 Years Later,” which was published on July 15, 2011, in the Journal of Pediatric Psychology, looked for a possible association between exposure to thimerosal-containing vaccines before birth or in the first seven months of life and neuropsychological function at ages 7-10 years old.

o This study used the same data from the study by Thompson et al published in the September 27, 2007 New England Journal of Medicine.  The original study evaluated 1,047 children ages 7-10 and their biological mothers and concluded that ethyl mercury exposure from thimerosal-containing vaccines and immunoglobulins does not affect neuropsychological functioning at ages 7-10 years.

• The authors concluded that that the weight of the evidence in this study does not support a causal association between early exposure to mercury from thimerosal-containing vaccines and immune globulins administered prenatally or during infancy and neuropsychological functioning at the age of 7–10 years for any of the other neuropsychological outcomes assessed.

The Science

• Safety of Vaccines Used for Routine Immunization in the United States

• IOM Report: Adverse Effects of Vaccines: Evidence and Causality, 2011

• CDC Studies on Vaccines and Autism [pic] [PDF - 30 KB]

• Hurley AM, Tadrous M, Miller ES. Thimerosal-containing vaccines and autism: a review of recent epidemiologic studies[pic]. J Pediatr Pharmacol Ther. 2010 Jul;15(3):173-81.

• Price CS, Thompson WW, Goodson B, Weintraub ES, Croen LA, Hinrichsen VL, Marcy M, Robertson A, Eriksen E, Lewis E, Bernal P, Shay D, Davis RL, DeStefano F. Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism[pic]. Pediatrics. 2010 Oct;126(4):656-64. doi: 10.1542/peds.2010-0309. Epub 2010 Sep 13.

• Hornig M, Briese T, Buie T, Bauman ML, Lauwers G, et al. (2008) Lack of Association between Measles Virus Vaccine and Autism with Enteropathy: A Case-Control Study.[pic] PLoS ONE 3(9): e3140. doi:10.1371/journal.pone.0003140

• McMahon AW, Iskander JK, Haber P, Braun MM, Ball R. Inactivated influenza vaccine (IIV) in children < 2 years of age: Examination of selected adverse events reported to the Vaccine Adverse Event Reporting System (VAERS) after thimerosal-free or thimerosal-containing vaccine.[pic] Vaccine 2008;26(3):427–429.

• Pichichero ME, Gentile A, Giglio N, et al. Mercury levels in newborns and infants after receipt of thimerosal-containing vaccines [pic] [PDF - 404 KB][pic]. Pediatrics 2008;121:e208-214.

• Schechter R, Grether JK. Continuing increases in autism reported to California’s developmental services system: mercury in retrograde[pic]. Arch Gen Psychiatry 2008;65:19-24.

• Thompson WW, Price C, Goodson B, et al. Early thimerosal exposure and neuropsychological outcomes at 7 to 10 Years.[pic] N Engl J Med 2007;357:1281-92.

• William W Thompson et al publish Early Thimerosal Exposure and Neuropsychological Outcomes at 7 to 10 Years[pic].  N Engl J Med 2007; 357:1281-1292

• Mandell DS, Thompson WW, Weintraub ES, Destefano F, Blank MB. Trends in diagnosis rates for autism and ADHD at hospital discharge in the context of other psychiatric diagnoses[pic]. Psychiatr Serv. 2005 Jan;56(1):56-62.

• Burbacher TM, Shen DD, Liberato N, et al. Comparison of blood and brain mercury levels in infant monkeys exposed to methylmercury or vaccines containing thimerosal. Environ Health Perspect 2005;113:1015–21.

• DeStefano F, Bhasin TK, Thompson WW, Yeargin-Allsopp M, Boyle C (2004) Age at first measles-mumps-rubella vaccination in children with autism and school-matched control subjects: a population-based study in metropolitan Atlanta.[pic] Pediatrics 113: 259–266.

• Immunization Safety Review Committee. Immunization Safety Review. Vaccines and Autism[pic] Board of Health Promotion and Disease Prevention, Institute of Medicine (National Academy Press, Washington, DC, 2004).

• Hviid A, Stellfeld M, Wohlfahrt J, Melbye M. Association between thimerosal-containing vaccine and autism [pic] [PDF - 145 KB][pic]. JAMA 2003;290:1763–6.

• Paul Stehr-Green, et al, publish Autism and Thimerosal-Containing Vaccines, Lack of Consistent Evidence for an Association, American Journal of Preventive Medicine[pic]. American Journal of Preventive Medicine, Volume 25, Issue 2, Pages 101-106, August 2003.

• Thomas Verstraeten, et al, publish Safety of Thimerosal-Containing Vaccines: A Two-Phased Study of Computerized Health Maintenance Organization Databases [pic] [PDF - 121 KB][pic], Pediatrics 2003.

• Pichichero ME, Cernichiari E, Lopreiato J, Treanor J. Mercury concentrations and metabolism in infants receiving vaccines containing thimerosal: a descriptive study.[pic] Lancet 2002;360(9347):1737–1741.

• Ball L, Ball R, Pratt RD. An assessment of thimerosal in childhood vaccines.[pic] Pediatrics 2001;107:1147–1154.

• Joint statement of the American Academy of Pediatrics (AAP) and the United States Public Health Service (USPHS)[pic]. Pediatrics 1999;104:568–9.

• Agency for Toxic Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services. Toxicological Profile for Mercury (Update). Atlanta, GA, 1999.

• Mahaffey KR. Methylmercury: A new look at the risks.[pic] Public Health Reports 1999;114(5):396–399, 402–413.

• Jacobs RL, Lowe RS, Lanier BQ. Adverse reactions to tetanus toxoid.[pic]Journal of the American Medical Association 1982;247(1):40–42.

• Förström L, Hannulksela M, Kousa M, Lehmuskallio E. Merthiolate hypersensitivity and vaccination.[pic] Contact Dermatitis 1980;6:241–245.

Other Helpful Resources

• Timeline: Thimerosal in Vaccines (1999--2010)

• Frequently Asked Questions about Thimerosal

• CDC’s vaccine safety thimerosal page

• CDC’s Concerns about Autism page

• FDA’s Thimerosal in Vaccines Questions and Answers

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