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"Thimerosal Exposure in Infants and Developmental Disorders: A Prospective Cohort Study in the United Kingdom Does Not Support a Causal Association"
Pediatrics, John Heron and Nick Andrews, PhD (September 2004)


Often referred to as the "UK Study." The worst study ever created? Every kid in the study got the same vaccines, so the study only considered timing differences. Wins award for most dishonest title, and got our lowest score.

Actual Question This Study Asked & Answered:

Q: Did children who all received DTP vaccine with thimerosal have higher or lower rates of developmental disorders based on when they got the shots?

A: No, except for an increase in reported tics.

Did the study look at unvaccinated children?


Conflict of Interest (from the study itself):

"Financial support for the establishment of the ALSPAC cohort was provided by the Medical Research Council, the Wellcome Trust, the UK Department of Health [the British CDC], the Department of the Environment, and DfEE, the National Institutes of Health, and a variety of medical research charities and commercial companies [vaccine makers]. Funding for this study was provided by the Department of Health [the British CDC]."

Ability to Generalize:

None. It only considered WHEN children all received the same vaccines, not "if."

Post-Publication Criticism:

Very high.

Scoring (Out of 40 possible points):

Asked the Right Question: -2

Ability to Generalize: -1

Conflict of Interest: 0

Post-Publication Criticism: -1

Total Score: -4

Choice Excerpt from the Study:

"The age at which doses of thimerosal-containing vaccines were administered was recorded, and measures of mercury exposure by 3, 4, and 6 months of age were calculated and compared with a number of measures of childhood cognitive and behavioral development covering the period from 6 to 91 months of age."


Every kid in our study got the same vaccines, and we only considered when they got them.

Guest Critic #1: John Stone, Researcher

Heron and Golding: erroneous premise, anomalous results

Heron and Golding’s paper is based on two false premises, and its results are therefore anomalous. The premises are (a) that they are studying the results of "low doses" of mercury, and (b) that the medium of thimerosal is less pernicious than other familiarly encountered forms of mercury:

"It has been suggested that low doses of ethylmercury might have a similar effect on childhood cognitive development as methylmercury; however, there is little evidence to support this claim. Moreover, ethylmercury is more quickly metabolized and evacuated from the body than methylmercury."

However, we are told in the very next paragraph:

"Current guidelines on safe exposure to thimerosal have been extrapolated from data on methylmercury and are varied, from 0.1 µg/kg/day of the Environmental Protection Agency in the United States to 0.47 µg/kg/day of the World Health Organization. Before the change to thimerosal-free vaccines, US children could have been exposed to levels as high as 187.5 µg by the time they were 6 months of age, exceeding the Environmental Protection Agency guidelines. In the United Kingdom, the only vaccines that contain thimerosal and have been routinely used in the past 2 decades are whole-cell diphtheria/tetanus/pertussis (wDTP) vaccine or diphtheria-tetanus (DT) vaccine and any combination vaccine containing wDTP or DT. Although the United Kingdom exposure is lower by 6 months, the accelerated United Kingdom primary immunization schedule of 2/3/4 months means that a maximum exposure of 75 µg may be received by 4 months of age."

So, in fact, these were not "low doses" of Thimerosal at all. Using US CDC growth charts [1,2] I have calculated by how many times approximately UK vaccination practice exceeded the US Environmental Protection Agency’s reference dose (RfD) for mercury: "Currently, US EPA uses an RfD of 0.1 micrograms/kg bodyweight/day as an exposure without ecognized effects" [3]. Each shot of DPT given at 2,3 and 4 months we are told contained approximately 25 micrograms of mercury, which is 250 times 0.1 microgram. In order to calculate the excess dose you need to divide 250 by the weight of the infant in kilograms. These are the results:

2 months: weight range 3.8-6.4kg: excess dose 40-66 times EPA RfD for mercury

3 months: weight range 4.5-7.4kg: excess dose 35-56 times EPA RfD for mercury

4 months: weight range 5.2-8.3kg: excess dose 30-48 times EPA RfD for mercury

It is impossible to imagine someone deliberately overdosing on a medical product -- except to harm themselves -- at this level, but this is not a therapeutic substance but a deadly neuro-toxin.

Furthermore, far from thimerosal being an exceptionally benign format for mercury manufacturers’ safety advice suggests precisely the opposite. I quote from Merck’s current European safety information:

"Very toxic by inhalation, in contact with skin and if swallowed. Danger of cumulative effects. Very toxic to aquatic organisms, may cause long-term adverse effects in aquatic environment."

"Keep away from food, drink and animal feeding stuffs. After contact with skin wash immediately with plenty of water. Wear suitable protective clothing. In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible). This material and its container must be disposed of as hazardous waste. Avoid release to the environment." [4]

A manufacturer’s safety data sheet (MSDS) for thimerosal from Amersham/US Bioscience mentions a long list of symptoms associated with autism:

"Chronic ingestion or excessive dosage may cause numbness, tingling of hands, feet, lips, ataxia, painful joints, constriction of visual fields, impaired hearing, emotional disturbances, spastic movements, incontinence, groaning, shouting, dizziness, lacrimation, hypersalivation, nausea, vomiting, diarrhea and constipation." [5]

Heron and Golding’s failure to detect any adverse effects is, therefore, quite as surprising as the practice of injecting infants with thimerosal in the first place.





[5] 02.pdf

Reprinted from Pediatrics.