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Thimerosal Containing Vaccines, Part I

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In the Dark

by F. Edward Yazbak MD, FAAP

This series on thimerosal-containing vaccines (TCV) is a critical review of the subject and what is known about it at this time. (Spring 2011)

Thimerosal is not my primary area of interest. I therefore promise to be extra careful documenting the facts and even more careful commenting on them.

Because the CDC only promotes vaccines and vaccination, the write-up about Thimerosal in vaccines on the CDC web site is relatively short:

Thimerosal is a mercury-containing preservative used in some vaccines and other products since the 1930's. There is no convincing evidence of harm caused by the low doses of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site. However, 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 is not exactly true. Thimerosal was not only used in some vaccines; it was used in most if not all vaccines “since the 1930’s”. It is only later that the mercury preservative was not used in Live Virus Vaccines (LVV) and even later that unit-dose vaccines without preservative became available, under duress.

The second sentence is no less problematic. Objective evidence of harm in vivo and in vitro is and has been available for some time, as I will show in Part III of this series. Whether the CDC will ever be convinced of that, is another story.

The last sentence of the statement is also somewhat misleading. In fact, the Joint Statement issued by the AAP and the PHS in July 1999 "established the goal of removing the vaccine preservative thimerosal as soon as possible from vaccines routinely recommended for infants.”

So in 2011, thimerosal has indeed not been removed from “vaccines”. It has been mostly eliminated from pediatric vaccines with some still containing traces of the preservative. Adult vaccines and a few pediatric inactivated influenza vaccines currently available in the United States contain as much of the preservative as they did before 1999.

The above suggests that each of the three sentences of the most visible CDC information on thimerosal in vaccines is not exactly accurate.

Whether the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed whole-heartedly or had to agree is another story that will be discussed later.


The FDA licenses vaccines and is at least in theory ultimately responsible for them.

An enormous amount of information about thimerosal on the FDA web site starts with information not too different from that on the CDC web site except that the FDA specifies that thimerosal was removed from “all vaccines routinely recommended for children 6 years of age and younger”.

Thimerosal is a mercury-containing organic compound (an organomercurial). Since the 1930s, it has been widely used as a preservative in a number of biological and drug products, including many vaccines, to help prevent potentially life threatening contamination with harmful microbes. Over the past several years, because of an increasing awareness of the theoretical potential for neurotoxicity of even low levels of organomercurials and because of the increased number of thimerosal containing vaccines that had been added to the infant immunization schedule, concerns about the use of thimerosal in vaccines and other products have been raised. Indeed, because of these concerns, the Food and Drug Administration has worked with, and continues to work with, vaccine manufacturers to reduce or eliminate thimerosal from vaccines.
Thimerosal has been removed from or reduced to trace amounts in all vaccines routinely recommended for children 6 years of age and younger, with the exception of inactivated influenza vaccine. A preservative-free version of the inactivated influenza vaccine (contains trace amounts of thimerosal) is available in limited supply at this time for use in infants, children and pregnant women…

Unlike the CDC, the FDA discussion of the subject is so exhaustive that one must wonder whether the goal was information or a veiled attempt at justification and or exoneration.

The United States Code of Federal Regulations (CFR) actually required the addition of a preservative to multi-dose vials of vaccines in January 1968.

“Products in multi-dose containers shall contain a preservative, except that a preservative need not be added to Yellow Fever Vaccine; Polio-virus Vaccine, Live Oral; viral vaccine labeled for use with the jet injector; dried vaccines when the accompanying diluent contains a preservative; or to an Allergenic Product in 50 percent or more volume (v/v) glycerin. [21 CFR 610.15(a)]

The CFR specified that the preservative used

.[s]hall be sufficiently non-toxic so that the amount present in the recommended dose of the product will not be toxic to the recipient, and in combination used it shall not denature the specific substance in the product to result in a decrease below the minimal acceptable potency within the dating period when stored at the recommended temperature. [21 CFR 610.15(a)]”


There were also several problems with the FDA statement. For the sake of brevity, only two will be discussed.

Under “Thimerosal as a preservative”, the FDA states:

“Prior to its introduction in the 1930’s, data were available in several animal species and humans providing evidence for its safety and effectiveness as a preservative (Powell and Jamieson 1931). Since then, thimerosal has been the subject of several studies (see Bibliography) and has a long record of safe and effective use preventing bacterial and fungal contamination of vaccines, with no ill effects established other than minor local reactions at the site of injection”

The statement suggests that before thimerosal was added to vaccines, Powell and Jamieson had shown that it was safe and effective. This is not exactly true because the FDA clearly states in the same document that Powell and Jamieson’s 1931 study “was not specifically designed to examine toxicity; 7 of 22 subjects were observed for only one day, the specific clinical assessments were not described, and no laboratory studies were reported.”

And then there is the mention about thimerosal being the subject of “several studies” and the annotation “see Bibliography” immediately followed by “and has a long record of safe and effective use preventing bacterial and fungal contamination of vaccines”, all in a chapter about “Thimerosal in Vaccines”.

Unlike most readers in a rush, I clicked on “Bibliography” to look at those studies I had never heard about. They were listed under the title:

“Studies on Safety and Effectiveness of Thimerosal”

The words “in vaccines” had disappeared and there were only 8 studies listed. The very first two studies were published in 1974, some 43 years after Powell and Jamieson and the most recent one, on preservatives in nasal preparations was published in 1989, over twenty years ago. Study # 3 was on urinary cytology and studies # 4, 5, 6 and 8 were on ophthalmological preparations. The two 1974 studies (# 2 and 7) dealt with development and standardization of the preservative in general.

There was in fact no study about the safety and efficacy of thimerosal in vaccines.


The second unconvincing FDA statement was under “Thimerosal Toxicity”. After listing the many known instances of toxicity of the preservative, the FDA decided to “prove” that thimerosal was safe by quoting a single reference, the 2002 study in Lancet by Pichichero et al.
The FDA proposed that the study proved that
“Blood levels of mercury did not exceed safety guidelines for methyl mercury for all infants in these studies. Further, mercury was cleared from the blood in infants exposed to thimerosal faster than would be predicted for methyl mercury; infants excreted significant amounts of mercury in stool after thimerosal exposure, thus removing mercury from their bodies. These results suggest that there are differences in the way that thimerosal and methyl mercury are distributed, metabolized, and excreted. Thimerosal appears to be removed from the blood and body more rapidly than methyl mercury.”

In fact, the study had several limitations affecting its conclusions:
  • Only 40 infants who received TCV were included, 20 aged 2 months and 20 aged 6 months
  • Just 21 infants who received thimerosal-free vaccines were used as controls
  • The injected mercury was judged as a range of mean mercury doses
  • Blood draws were done conveniently when the parents were able to bring the infants back
  • Among Hg-exposed infants, blood samples from twelve 2-month-old were collected from 8 and 21 days after vaccination and blood samples from thirteen 6-month-old infants were collected from 8 to 27 days after vaccination, when in all probability the Hg was no longer in the blood and had settled in tissues including the brain
  • The half life of thimerosal mercury, that seemed to have impressed someone at the FDA, resulted from pharmacokinetic calculations whose description was peppered with statements such as: we developed a prediction, the expected concentrations, half-lives of mercury ranging from 1 day to 45 days, we assumed, elimination of mercury from blood followed a single compartment model with first-order kinetics, possible half-life, the difference between the predicted and actual recorded concentrations in blood, reliable quantitation, and assumption that errors…

The extensive statement on the FDA web site did not include the most important fact of all: A safe range of level of exposure to ethyl mercury.

It is worth mentioning that in spite of the present obsession with the subject, responsible agencies have yet to agree on the supposedly safe levels for methyl mercury: The EPA estimate of 0.1 µg/kg body weight/day is only a fraction of the WHO estimate of 0.47 µg/kg body weight/day.


The FDA information included conclusions and recommendations by the Immunization Safety Review Committee of the Institute of Medicine.

In October 2001, the committee concluded:
  1. That although the hypothesis that exposure to thimerosal-containing vaccines could be associated with neurodevelopmental disorders is not established and rests on indirect and incomplete information, primarily from analogies with methylmercury and levels of maximum mercury exposure from vaccines given in children, the hypothesis is biologically plausible.
  2. That the evidence is inadequate to accept or reject a causal relationship between thimerosal exposures from childhood vaccines and the neurodevelopmental disorders of autism, ADHD, and speech or language delay.
Among other things, the committee recommended, “that full consideration be given by appropriate professional societies and government agencies to removing thimerosal from vaccines administered to infants, children, or pregnant women in the United States” and “that appropriate professional societies and governmental agencies review their policies about the non-vaccine biological and pharmaceutical products that contain thimerosal and are used by infants, children, and pregnant women in the United States.”

Unfortunately in 2004, with thousands of cases of autism having been filed, the same IOM committee decided, based on epidemiological studies that the “body of evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism, and that hypotheses generated to date concerning a biological mechanism for such causality are theoretical only.”

Multiple articles criticizing the above-mentioned epidemiological studies from Sweden, Denmark and the US have been published, including several by this writer.


For those interested, a bibliography review of adverse reports related to thimerosal was provided in a press release on March 17, 2002 by the well-known law firm of Waters and Kraus. [/DailyNews/March2002/Waters%2526KrausPressRelease3-17-02.htm]

Chronology of Thimerosal in Vaccines

In 1927, Morris Kharasch an Organic Chemist filed a patent application for an alkyl mercuric sulfur compound with “potential” antiseptic and antibacterial properties and assigns it to Eli Lilly and Co.

Two years later, Eli Lilly & Co. registered the product under the trade name Merthiolate.
[Other names for ethylmercurithiosalicylate sodium are Thimerasol, Thiomerosal; Thiomersal; Thimersalate; Thiomersalate; Merfamin; Merthiolate sodium; Mertorgan; Merzonin and Sodium ethylmercuric thiosalicylate …]
Thimerosal is 49.6 percent mercury by weight and is metabolized into ethylmercury and thiosalicylate.

As mentioned earlier, thimerosal has been the preferred preservative in vaccines since the late 1930s supposedly because of its ability to prevent contamination of multiple-dose vials by killing pathogenic organisms and fungi.

Years ago, I proposed that thimerosal was really added to vaccines to prevent contamination on the production line and not in the doctor’s office. In the fall of 2004, thousands of doses of influenza vaccine at Chiron Labs in the UK were condemned and discarded because of contamination with Serratia Marascans.

The FDA had found “serious problems of bacterial contamination” at the influenza vaccine plant in England in 2003, “16 months before British regulators effectively closed the site and impounded its flu shots because of fears they were tainted.”

For 50 years, we pediatricians obediently used thimerosal-laced vaccines and said nothing. Why we were fooled for so long will be explained later.

In 1980 and for reasons not as yet completely clear, the FDA suddenly started examining over-the-counter (OTC) products containing thimerosal. Citing concerns about toxicity and inefficacy, the agency then began banning some OTC thimerosal-containing ointments and topical products.

In 1991, world-renowned vaccine developer Maurice Hilleman PhD sent a memo to Dr. Gordon Douglas, Head of Merck’s Vaccine Division telling him that Sweden is requiring thimerosal-free single-dose packaging of all products as soon as can be reasonably achieved. Hilleman wrote: “For babies: The 25 µg of mercury in a single 0.5 ml dose and extrapolated to a 6 lb baby would be 25 X the adjusted Swedish daily allowance of 1.0 µg for a baby of that size …. If 8 doses of thimerosal-containing vaccine were given in the first six months of life (3 DPT, 2 HIB and 3 Hepatitis B), the 200 µg of mercury given, say an average size of 12 lbs pounds would be about 87 X the Swedish daily allowance of 2.3 µg of mercury for a baby of that size.”

Dr. Hilleman also told Douglas that in order of toxicity, methyl and ethyl salts were most toxic. Mercury vapor was intermediate and inorganic salts least toxic.

[Interestingly, we still have “experts” in 2011 who still claim that ethyl mercuric compounds are “safer” than methyl compounds.]

Merck and other manufacturers obliged and immediately produced mercury-free vaccines for Scandinavian infants and children.

Our U.S. children were not as lucky. Not only did they keep getting thimerosal-laced pediatric vaccines, they actually received more of them, including a dose in the nursery.

Six years later, New Jersey Representative Frank Pallone cleverly attached a short amendment of 133 words to the FDA reauthorization bill 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 in the list” within two years.

The Food and Drug Administration Modernization Act (FDAMA) was signed into law on November 21, 1997.

On October 22, 1998, the FDA ban on the use of several other OTC mercury-containing compounds went into effect because A. the safety and effectiveness of the mercury components had not been established and B. the manufacturers had not submitted data to the contrary.

During the following months, the FDA’s best experts from the Center for Biologics Evaluation and Research (CBER) researched and discussed the issue in depth. After they were done, they had to acknowledge that because safety studies about ethylmercury were non-existent and because toxic levels of the compound were still unknown, they were unable to determine how toxic the thimerosal concentrations of up to 0.01 percent in more than 30 US-licensed vaccines were.

Even though they did not agree on its toxicity level, the FDA, the EPA and the Agency for Toxic Substances and Disease Registry (ATSDR) knew much more about methyl mercury toxicity.

After much deliberation, CBER decided to consider thimerosal’s toxicity in reference to the EPA’s methyl mercury guidelines. It is then that it became evident that the mercury content of pediatric vaccines administered during the first six months of life exceeded the EPA reference dose (RfD) for methyl mercury of 0.1 micrograms per kilogram body weight per day (µg/kg/day).

With the FDAMA deadline of Nov. 27, 1999 approaching, things heated up. Something needed to be urgently done concerning thimerosal in vaccines and more specifically pediatric vaccines.

In early June 1999, Neal Halsey, MD, FAAP, chairman of the American Academy of Pediatrics Committee on Infectious Diseases and Director of the Institute for Vaccine Safety at Johns Hopkins University was invited to a meet with the FDA team. At the meeting, he was provided with the latest findings and alerted about the urgency to do something regarding the amounts of thimerosal in pediatric vaccines.

Dr. Halsey became alarmed and discussed the subject with his committee and the AAP hierarchy.

At a National Immunization Conference held on June 25, 1999, Dr. Halsey met with key people at the CDC and realized that they were looking at the situation from a totally different angle. They were mostly interested in safeguarding their excellent vaccination programs while Halsey and most pediatricians were more worried by the day about the serious ethical and legal implications of the mercury in vaccines issue.

After much haggling the two sides agreed that:
1. Thimerosal had to be removed from pediatric vaccines.

2. A “careful” joint public statement by the Public Health Service (PHS) and the American Academy of Pediatrics (AAP) would be issued to pre-empt the FDA announcement scheduled for sometime in July (1999) and the inevitable press frenzy it was certain to create.

On June 28, 1999, the Interagency Vaccine Group (IAG) held a conference to review the updated FDA risk assessment information and created a special workgroup to examine all thimerosal related matters. Meanwhile, officials from the CDC immunization branch met in a hurry with their own toxicologists and with the vaccine companies’ risk assessors.

Because of the urgency of the situation, Dr. Halsey and leading AAP officials organized an “informal” meeting to be held on June 30, 1999 at the AAP offices in Washington, D.C. and invited “everyone”. This avoided the long delays required for a formal meeting.

Disagreements still existed between the organizations and even within the organizations. The AAP committee on Infectious Diseases and the AAP committee on Environmental Health were still as divided on the issue as were the agencies and the Academy.

The proposed actions ranged from immediately stopping administration of all vaccines containing thimerosal to infants six month-old or younger to encouraging the elimination of thimerosal by vaccine manufacturers.

It was decided at the end of the long and tumultuous session that no statement would be issued until after the July 4 weekend when a PHS and AAP unified public statement would be released.  

A good summary of that unified public statement by the PHS and the AAP can be found in the July 14, 2000 MMWR. []

As formulated in the joint statement, the goal was to remove thimerosal from vaccines routinely recommended for infants as soon as possible while reassuring everyone that no evidence existed of any harm caused by low levels of thimerosal in vaccines.

The groups had at last agreed to remove thimerosal from pediatric vaccines but very clearly, many had done so under duress.

Slowly, US babies received less and less thimerosal in their vaccines.

The 1999 decision had little economic effect on the manufacture of thimerosal and of thimerosal-containing vaccines. Thimerosal is still being produced in enormous quantities and millions of thimerosal-laced doses of vaccines are still being packaged and shipped daily … to “Third World” countries.


I do not know how many of my pediatric colleagues are as upset as I am about being duped into believing for so long that the quantities of mercury we injected into infants and children were insignificant.

I know for sure that Dr. Neal Halsey was absolutely right when he said:

''In most vaccine containers, thimerosal is listed as a mercury derivative, a hundredth of a percent. And what I believed, and what everybody else believed, was that it was truly a trace, a biologically insignificant amount. My honest belief is that if the labels had had the mercury content in micrograms, this would have been uncovered years ago. But the fact is, no one did the calculation.''

In the third slide of a power- point presentation titled “Commentary on Potential Risk from Thimerosal for Infants”, Dr. Halsey mentioned that excellent point again.

In the following slide, Dr. Halsey listed situations where thimerosal (in large doses) was proved to be neurotoxic.

The rest of the presentation is full of useful information.


I find the following disturbing:
  • That the CDC, the FDA and other organizations are still downplaying the problem by stating that thimerosal “has been used since the 1930’s with no convincing evidence of harm, except for local reactions”
  • That some “experts” still insist on comparing the danger from injecting TCV into infants to eating half a tuna fish sandwich
  • That certain TCV vaccines that were not routinely administered during pregnancy in the past, are now not only recommended but encouraged
  • That when Scandinavian countries chose to remove mercury from vaccines, US vaccine makers immediately complied yet never considered doing the same for infants in the United States until forced to do so years later
  • That to this day, vaccine companies are still producing millions of doses of TCV and shipping them to "Third World" countries

This last atrocious state of affairs is the subject of Part II of this series.

In Memoriam: Philip B Rudnick PhD ~ December 23, 2010

F. Edward Yazbak MD, FAAP
Falmouth, Massachusetts

Thimerosal Containing Vaccines, Part II - WHO by F. Edward Yazbak MD, FAAP

Thimerosal Containing Vaccines, Part III - The Convincing Evidence by F. Edward Yazbak MD, FAAP