[back] Thimerosal

The Mercury Memo

By  F. Edward Yazbak, MD, FAAP


Falmouth, Massachusetts, USA


    * Adding a mercury preservative to vaccines over six decades ago was reckless.

    * Not offering thimerosal-free vaccines to American children during the nineties - when those vaccines were available for Scandinavian children - was wrong.

    * Ultimately, the truth comes out.

 1. Thimerosal

 Thimerosal is a water-soluble organic mercury compound that has been used as a preservative in vaccines andpharmaceutical products –from eye drops to hemorrhoidal ointments- since the late 1930’s. It contains approximately 49% mercury and is metabolized in the body to ethylmercury and thiosalicylate. The product is also called Elicide, Mercurorothiolate, Merfamine, Merthiolate, Mertorgan, Merzonin, Thimerosalate, Thimersal and Thiomersalate. According to the CDC, Thimerosal has been used in injectable vaccines because “it is effective in killing bacteria and in preventing bacterial contamination, particularly in opened, multidose containers”.

 The mercury in Thimerosal has received much deserved attention lately- at last. The Thiosalicylate end-product has not garnered the same interest. It probably should.

 Since the FDA Modernization Act of 1997, the Food and Drug Administration had raised concerns that infants who received multiple thimerosal-containing vaccines could be actually subjected to a mercury exposure exceeding safe federal guidelines.

 In 1999, the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) recommended that, because any potential risk from mercury is of concern, and the elimination of exposure to mercury in the form of thimerosal from vaccines is feasible, thimerosal should be removed from pediatric vaccines as soon as possible. They maintained – and still do- that there was no convincing evidence of harm caused by the low levels of thimerosal in vaccines.

 As of September 2001, there were still some 66,000 doses (5.5%) of pediatric vaccines with Thimerosal in the 225 sites that were surveyed in 16 states.

 Except for the flu vaccine, all presently-available pediatric vaccines are supposed to be Thimerosal-free. In many cases, this means that the “preservative” was used in the manufacturing process and then removed. The vaccine manufacturers concede that sometimes “traces” of Thimerosal remain.

 The words “Thimerosal” and “Mercury” have become so threatening to the Industry that the new pediatric vaccine labels are stamped “Preservative-Free” to clearly indicate that they are indeed “Thimerosal or Mercury-Free”. Some industry consultant must have been concerned about their mere presence on the label - even if followed by the word “Free”.

 (Oops! Now that little secret is out!)

 Concerns about the efficacy of Thimerosal have also been raised. The fact that 50 million doses of Chiron British-manufactured flu vaccine were banned last summer because of bacterial contamination proves that the famous “preservative” even failed at the production line level.

 In March 2005, the CDC still states that “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.”

 A “Special Article” by Offit and Jew, in the December 2003 issue of PEDIATRICS, entitled “Addressing Parents’ Concerns: Do Vaccines Contain Harmful Preservatives, Adjuvants, Additives, or Residuals?” seems to support the CDC’s statement. The two authors Paul A. Offit, MD and Rita K. Jew, PharmD are associated with the Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine where Dr. Offit is Chief, Section of Infectious Diseases and the Henle Professor of Immunologic and Infectious Diseases.

 The summary of the “Special Article” concludes: “However,quantities of mercury, aluminum, formaldehyde, human serum albumin,antibiotics, and yeast proteins in vaccines have not been foundto be harmful in humans or experimental animals. “

2. Tuna on Rye

 Mercury in the air, on the ground and under water has been an Environmental Protection Agency (EPA) concern for decades.

 In 1974, Congress passed the Safe Drinking Water Act. The EPA established Maximum Contaminant Level Goals for metals and set up the MCLG for mercury in drinking water at 2 parts per billion (ppb). Link

 The EPA set the maximum recommended consumption limit for mercury in ingested foods at 0.1 microgram/kg/day.

 Mercury in consumed foods has obviously also been an FDA concern. It is usually in the form of methyl mercury and most often found in fish. Although the FDA has been closely monitoring mercury in fish since 1990, it is only lately that the danger of excessive fish consumption by pregnant women and children has been publicized.

3. Methyl & Ethyl

The damage to neurons by mercury is very graphically demonstrated in a short video showing an experiment carried out at the School of Medicine, University of Calgary.

 Click on  <Rapid Degeneration of neurons in the presence of Mercury.>

 Although there is universal agreement that mercury is dangerous, whether it is in the air we breathe, the water we drink or the tuna fish sandwich we have for lunch, the CDC has insisted that it is only because it is in the form of methyl mercury while the mercury we have injected in infants for six decades and in newborns during the nineties, could not have possibly hurt them because and only because it is metabolized into ethyl mercury.

 Logically one should not need to “prove” how flawed this argument is. Nevertheless, there have been many studies showing that ethyl mercury is indeed toxic, particularly in the large doses administered simultaneously to small infants.

 The relative toxicity of both organic mercury compounds was compared in experimental animals by Magos et al as early as 1985. (1) Ethyl mercury in a 20% higher dose was more neurotoxic than methyl mercury.

 Many parents of permanently damaged children with acquired autism and developmental problems who witnessed their children literally disappear in front of their eyes started researching the subject of mercury in vaccines themselves. Their initial and landmark article: “Autism: a novel form of mercury poisoning” was published in 2001(2) and was followed by others (3-7). In addition, several therapeutic modalities aimed at decreasing the mercury burden in certain children with autism has been followed with remarkable clinical functional improvement.

 More recently (June 2004), Hornig et al published a convincing animal study in which autoimmune disease-sensitive mice showed growth delay, reduced locomotion, exaggerated response to novelty and specific brain changes when exposed to thimerosal challengesmimicking routine pediatric immunizations.(8)

 Geier & Geier also provided the supporting epidemiological studies on the subject. (9-12)

 Parents and researchers have wondered for some time why autism suddenly appeared - literally out of the blue- in the early forties, shortly after Thimerosal was added to vaccines and how it increased with the increasing number of pediatric vaccinations and more so in the United States after the introduction of the HIB and Hepatitis B vaccinations.

 The CDC, physicians groups and the pro-vaccine lobby closed ranks and denied the suggestion.

 Several epidemiological studies were furtively produced in the US, Scandinavia and Great Britain - and obviously greatly advertised – to “prove” that the use of thimerosal in pediatric vaccines was not associated with any serious neuro-developmental problems in general and autism in particular. A single issue of PEDIATRICS (September 2004) contained THREE studies to that effect.

 Some of those epidemiological studies were the “evidence” an Institute of Medicine Special Committee needed in 2004 to “decree” that Thimerosal was not in any way responsible for the autism epidemic in spite of the fact that the flaws in the studies in question had been quickly reported after their publication.

 The fact is that even the most perfect epidemiological studies CANNOT prove a negative – “That mercury in vaccine does NOT cause autism”.  Fearing the worse, certain Senators and Congressmen furtively introduced legislation after legislation and added amendments in the middle of the night, to try to “immunize” the manufacturer of the infamous mercury preservative and the vaccine producers who were rendering a service of National and Worldwide importance. Others, seeing the disastrous damage in their community and thinking of their constituents first - rather than the rich drug companies - introduced legislation banning the use of Thimerosal from all vaccines and medicinal products.

4. The Hilleman memo of 1991

 Maurice R. Hilleman Ph.D. is a recognized authority in the field of vaccines having developed over 40 vaccines and published more than 480 original articles in the fields of virology, epidemiology, immunology, and infectious diseases.

 In an August 1999 article he was referred to as: “The Man who saved your life-Maurice R. Hilleman …”

 Dr. Hilleman has received many honors and medals during his long and remarkable professional career including the National Medal of Science (President Reagan), the Distinguished Service Medal for Research, the Albert B. Sabin Gold Medal and Lifetime Achievement awards, the Special Lifetime Achievement Award from the Children's Vaccine Initiative of the World Health Organization, the Maxwell Finland Award for Scientific Achievement of the National Foundation for Infectious Diseases and the Lasker Medical Research Award.

 Recently, a 1991 confidential memo on thimerosal and vaccines from Dr. Hilleman to Dr. Gordon Douglas, the head of Merck’s vaccine division at the time, has been made public.

  So far, this memo has received the silent treatment. More likely than not, we are just witnessing a calm before the inevitable storm, in a country where there are more than a million lawyers.  When - not if - a few of those lawyers decide to go forth, many people in high ranking positions will experience the toxicity of Thimerosal on their own nervous systems - firsthand.

 Being “THE Authority” Dr. Hilleman must have thoroughly reviewed the whole issue of thimerosal in vaccines – and agonized over it - before writing his memorable memo to the head of the vaccine division. He must also have chosen his words very carefully.

 The following selections from his 7-page 1991 memo are well worth a closer look.

4.1 The Problem

 Section 1 (P. 1) “The regulatory control agencies in some countries, particularly Scandinavia (especially Sweden) but also UK, Japan, and Switzerland have expressed concern for thimerosal, a mercury preservative, in vaccines. Some countries require absence of thimerosal from single-dose package. This trend will probably spread… Sweden is requiring thimerosal free single-dose packaging of all products as soon as can be reasonably achieved. The deadline for DT is January, 1992…”


     * Dr. Hilleman starts his memo by stating that the “regulatory agencies” in certain countries expressed concerns about Thimerosal in vaccines. One must wonder why the US regulatory agency did not have the same concerns in 1991.

    * Scandinavian countries acted in 1991 and Sweden set a deadline. The UK expressed concerns but did not act and infants in the United Kingdom were exposed to thimerosal at 2, 3 and 4 months of age until 2004. In the US, a 2, 4 and 6 months schedule was used.

    * When health authorities required the thimerosal-free vaccine, the Industry delivered.

    * In 1991, the world’s expert on vaccines expected that “the trend will probably spread”. Why it took so many years for the CDC to just “recommend” that the mercury preservative be removed from the pediatric vaccine formulations is unknown.

 4.2 The immediate concern

 Section 3 (P. 2): “The focal point for present concern is in Scandinavia…The immediate Merck concern is to be able to qualify for sale of single-dose products in Sweden and in Norway and Denmark…The public awareness has been raised by the sequential wave of experiences in Sweden including mercury exposure from additives, fish, contaminated air, bird death from eating mercury-treated seed grains, dental amalgam leakage, mercury allergy, etc…In some instances, public immunization programs may be endangered by public refusal to accept vaccines with thimerosal”

 Comments: (In 1991)

     * Merck’s primary and immediate priority was to market thimerosal-free vaccines to the three Scandinavian countries

    * Scandinavians believe that thimerosal should not be injected in people and that all mercury compounds should be avoided whether they are in vaccines (Ethyl) or in fish and the environment (Methyl)

    * Hilleman is confident that he can produce thimerosal-free vaccines

    * Hilleman is willing and happy to conform to the market needs in Scandinavia.

 4.3 The relative toxicity 

 Section 5 (P. 3): Hilleman rates the toxicity of mercury compounds as follows:

Most toxic: Methyl and ethyl salts

Intermediate: Mercury vapor

Least toxic: Inorganic mercury salts.

Comments: None needed

4.4 The toxicological perspective

 Section 6 e (P 5)

 For babies:  “The 25 µg of mercury in a single 0.5 ml dose and extrapolated to a 6 lb baby would be 25X the adjusted Swedish daily allowance of 1.0 µg for a baby if that size… If 8 doses of thimerosal-containing vaccine were given in the first 6 months of life (3 DPT, 2 HIB and 3 Hepatitis B) the 200 µg of mercury given, say an average size of 12 lbs would be about 87X the Swedish daily allowance of 2.3 µg of mercury for a baby of that size”


     * Hilleman concedes that in 1991, the available (US) pediatric vaccines – if administered according to the recommended schedule – would expose infants during the first six months of life to 87 times more mercury than the Swedish safe standards.

    * The mercury load on American babies was unacceptable in Scandinavia.

    * During the nineties, the recommended pediatric immunization schedule in the United States for the first six months of life included 3 doses of DTP/DTAP, 3 doses of HIB (and not 2) and 3 doses of Hepatitis B vaccine.

    * The US Hepatitis B vaccine contained 12.5 µg of mercury per dose and not 25 µg.

    * In fact, the potential mercury load for US infants was 187.5 µg by the age of six months- 82 times more than what Scandinavian children received in their first 6 months of life.

 Those who defend Thimerosal in vaccines and claim that it never hurt a baby, like to reassure parents by arguing that the injected amount of the mercury “preservative” represents “only” about one microgram of mercury a day - not a significant amount.

 The fact is that between 1991 and 1999, the 187.5 µg of mercury were NOT EVENLY DISTRIBUTED over the first 180 days of the baby’s life, so the 1µg/day argument is not valid. At the 2, 4 or 6 month-visit, the infant potentially received 62.5 µg of mercury in seconds – DTP (25µg) + HIB (25µg) + hepatitis B vaccine (12.5µg).  This represents an enormous amount of mercury introduced in a few seconds in a little baby whether he is Swedish, American or Sudanese and not withstanding the Pichichero study. (13)

 In addition, in the United States, the initial dose of hepatitis B vaccine with its 12.5µg of mercury was usually injected into newborns hours after they were born. Vaccination schedules usually start at six weeks of age for puppies and at 8 weeks for kittens.

 Universal Hepatitis B vaccination

 Pregnant women are usually screened for hepatitis B at their first obstetrical visit. Extreme vigilance should be exercised so that all expectant women are tested and those with the disease identified. Infants born to mothers who have hepatitis B or are hepatitis B carriers are at high risk and should receive hepatitis B immunoglobulin as soon as possible after birth - promptly followed by the first of three doses of hepatitis B vaccine.

 In the fall of 1991, the CDC announced the introduction of universal hepatitis B vaccination: The vaccination of ALL Infants starting at birth. The vaccination program was detailed in the MMWR report of November 22, 1991: <<Hepatitis B Virus: A Comprehensive Strategy for Eliminating Transmission in the United States Through Universal Childhood Vaccination: Recommendations of the Immunization Practices Advisory Committee >>

 (The whole report is worth reading regardless of one’s feeling on the subject.)

 Many well-informed scientists and certainly thousands of parents have questioned the logic behind the recommendation and the need to vaccinate infants who are not at any risk, starting at birth, particularly when the acquired immunity was not expected to last till the age of risky behavior.

 Three doses of the new recombinant vaccine were recommended for all US infants, regardless of their mothers’ Hepatitis B surface antigen status and the first dose was to be administered soon after birth except in the case of small prematures. One of the two available pediatric preparations was manufactured by Merck, Hilleman’s firm. It was available as a single dose unit and contained 12.5 µg of mercury until 1999, when it was replaced by a preservative-free product - in the United States.

 It is unclear why the preservative was ever needed in the single-dose unit.

 The autism angle

 Until lately, certain people were still denying that autism had increased in the United States during the nineties.

 The true and consistent increase in autism and autistic spectral disorders (ASD) in US schools has been thoroughly documented through the annual reports of the US Department of Education (DOE) to Congress. In 1991-1992, the DOE reported that there were 5,415 students with autism aged 6 to 21 in US schools. That number increased relentlessly by about 20% a year and reached 140,920 in school-year 2003-2004. The DOE started listing autism as an independent entity starting in 1991 (14, 15)

 In January 2004, an Autism A.L.A.R.M, was issued by HHS, CDC and AAP reporting that autism (and ASD) affected 1 in 166 children in the United States. In addition, 1 in every 6 children had a developmental or behavioral problem.

 On February 9, 2004 a special committee of the Institute of Medicine (IOM) decreed that thimerosal does not cause autism or indeed any harm at all. They based their decision on epidemiological studies, three of which were from Scandinavia. (16, 17, 18) The three studies were submitted for publication to three well-known US Medical Journals, peer-reviewed and published.

 It is certainly interesting that the (American) reviewers for the journals and the (American) members of the IOM Immunization Safety Review Committee examined the Scandinavian findings and evidence and believed that that they were relevant to the situation in the United States, when they should have known that the prevalence of autism was so much higher in the United States and that Scandinavian infants received fewer vaccines in the first year of life (6 compared to 12) – none with mercury.

 Unfortunately, the flawed conclusions of the Immunization Safety Review Committee Meeting of February 2004 are destined to be widely quoted in medical and legal circles. They certainly should not be and in fact, the whole report of the meeting should be withdrawn by the IOM.

 Now that the Hilleman memo has been made public, American parents will undoubtedly be wondering why the CDC waited so long to act and why a leading vaccine company based in New Jersey produced mercury-free vaccines for Scandinavia in 1991- when it had just launched a new single-dose preparation with Thimerosal for use in newborns and infants in the United States. More importantly, how is it that same company was able to deliver a Thimerosal-free hepatitis B vaccine in just a few weeks – following the CDC recommendation of  1999? 


     * A mercury “preservative” has been added to some injected vaccines for decades

    * It has been mostly removed from pediatric preparations in the US since 1999

    * The US health authorities still claim that it was safe

    * The Scandinavian health authorities have disagreed and have mandated thimerosal-free vaccines since the early nineties

    *  Mercury-free injectable vaccines manufactured in the United States were exported for years before they were available here at home

    * Parents in the United States have every right to be confused and angry

    * The Institute of Medicine should withdraw the 2004 Immunization Safety Review Committee Report and order a new meeting to examine real evidence

    * Compensation for families of mercury-injured children  with autism is justified and appropriate


 1. Magos L, Brown AW, Sparrow S, Bailey E, Snowden RT, Skipp WR. The comparative toxicology of ethyl- and methylmercury.Arch Toxicol. 1985 Sep;57(4):260-7.PMID: 4091651

 2. Bernard S, Enayati A, Redwood L, Roger H, Binstock T. Autism: a novel form of mercury poisoning. Med Hypotheses. 2001 Apr;56(4):462-71.  PMID: 11339848

 3. Blaxill MF, Redwood L, Bernard S. Thimerosal and autism? A plausible hypothesis that should not be dismissed. Med Hypotheses. 2004;62(5):788-94. PMID: 15082108

 4. Bernard S.Association between thimerosal-containing vaccine and autism. JAMA. 2004 Jan 14;291(2):180; PMID: 14722136

 5. Bernard S, Enayati A, Roger H, Binstock T, Redwood L.The role of mercury in the pathogenesis of autism. Mol Psychiatry. 2002;7 Suppl 2:S42-3. Review. PMID: 12142947

 6. Blaxill MF.Concerns continue over mercury and autism.Am J Prev Med. 2004 Jan;26(1):91; PMID: 14700719 

7. Holmes AS, Blaxill MF, Haley BE.Reduced levels of mercury in first baby haircuts of autistic children. Int J Toxicol. 2003 Jul-Aug;22(4):277-85. PMID: 12933322

 8. Hornig M, Chian D, Lipkin WI. Neurotoxic effects of postnatal thimerosal are mouse strain dependent. Mol Psychiatry. 2004 Sep;9(9):833-45. PMID: 15184908

 9. Geier DA, Geier MR.An assessment of the impact of thimerosal on childhood neurodevelopmental disorders. Pediatr Rehabil. 2003 Apr-Jun;6(2):97-102. PMID: 14534046

 10. Geier MR, Geier DA.Neurodevelopmental disorders after thimerosal-containing vaccines: a brief communication. Exp Biol Med (Maywood). 2003 Jun;228(6):660-4. PMID: 12773696

 11. Geier DA, Geier MR.A comparative evaluation of the effects of MMR immunization and mercury doses from thimerosal-containing childhood vaccines on the population prevalence of autism. Med Sci Monit. 2004 Mar;10(3):PI33-9. PMID: 14976450

 12. Geier D, Geier MR.Neurodevelopmental disorders following thimerosal-containing childhood immunizations: a follow-up analysis.Int J Toxicol. 2004 Nov-Dec;23(6):369-76. PMID: 15764492

 13. Pichichero ME, Cernichiari E, Lopreiato J, Treanor J. Mercury concentrations and metabolism in infants receiving vaccines containing thiomersal: a descriptive study. Lancet. 2002 Nov 30;360(9347):1737-41.

 14. Yazbak FE. Autism in the United States: A Perspective  J .Am Phys Surg  2003; 8(4) 103-108

 15. link

 16. Hviid A, Stellfeld M, Wohlfahrt J, Melbye M. Association between thimerosal-containing vaccine and autism. JAMA. 2003; 290(13): 1763-1766

 17. Madsen KM, Lauritsen, MB, Pedersen CB, Thorsen P, Plesner AM, Andersen PH and Mortensen PB. Thimerosal and the Occurrence of Autism: Negative Ecological Evidence From Danish Population-BasedData. Pediatrics. 2003;112(3):604-606

 18. Stehr-Green P, Tull P, Stellfeld M, Mortenson PB, Simpson D. Autism and thimerosal-containing vaccines: lack of consistent evidence for an association. Am J Prev Med. 2003;25(2):101-106

 F. Edward Yazbak, MD

TL Autism Research

Falmouth, Massachusetts 02540