Is mercury present in today’s vaccines? If yes, is the amount harmful? Why was mercury used as an ingredient in vaccines?
Historical use of thimerosal in vaccines.
Mercury has been added to vaccines to preserve and prevent bacterial contamination of multi-dose shots (1,2). It is present in vaccines in the form of a compound known as thimerosal. Once injected into the body via intramuscular injection, it is rapidly broken down into thiosalicylate and ethylmercury (1). Ethylmercury is an organic toxic mercury compound and the focus of the debate over mercury in vaccines.
In 1999, the American Academy of Pediatrics and the Public Health Service called for mercury to be removed from vaccines because it was found that the amount of mercury in vaccines given to infants exceeded the EPA reference dose or per day exposure threshold for methylmercury. Note that a reference dose for ethylmercury has never been experimentally determined.
EPA Reference Dose = 0.1 mcg/kg/day (2,3,4).
Though the thimerosal content of most vaccines was reduced to “trace amounts” (0.3-1.0mcg mercury per dose) or eliminated after 1999, unfortunately, the total amount of mercury a child from 6 months to 18 years of age will receive through the recommended CDC vaccination schedule, has increased since the AAP called for its removal (6). The reason for this was that in 2002, the CDC began recommending that pregnant women and infants as young as 6 months get annual flu shots at 1-2 doses per season.
Current use of thimerosal in vaccines.
Current vaccines approved for use in the US which contain mercury are multi-dose influenza vaccines. Thimerosal-preserved “multi-dose” flu shots contain 25mcg mercury per dose. However, some vaccines labeled “preservative free” or “thimerosal free” contain trace amounts of mercury (2). Children from 6 months to 35 months of age receive a half-dose of the flu vaccine. Children three years of age or older, and adults, receive a full dose. 21-36 million multi-dose flu shots were produced for the US in the 2017-2018 season.
Regarding mercury content of multidose flu vaccines, per vaccine, a six-month-old will receive 12.5mcg mercury (a half dose) which is over 16x the safe dose per the EPA (see calculations below). A three-year-old will receive 25mcg mercury via the flu shot, which is almost 18x the safe dose per the EPA. At 25mcg mercury per dose, an individual would need to weigh over 550lbs to approach the reference dose level.
Average 6-month-old infant weight = 16.5lbs or 7.5kg
EPA reference dose or allowable limit for average 6-month-old:
7.5kg (0.1mcg/kg/day) = 0.75mcg/day
1/2 dose flu shot for children ages 6-35 months contains 12.5mcg mercury.
(12.5mcg) / (0.75mcg) = 16.67x EPA reference dose
Methylmercury vs. Ethylmercury.
Form of the mercuric compound (e.g. organic vs. inorganic) and route of exposure (dermal, inhalation, ingestion, injection) dictates toxicity. Organic mercury is lipophilic and can readily pass through lipid membranes of cells, while inorganic mercury is not readily absorbed. The digestive tract is a barrier to absorption of toxic substances, whereas injection of a substance bypasses natural bodily defenses and is fully absorbed. Therefore, the form of mercury and route of exposure is important when assessing toxicity (7,8).
Methylmercury and ethylmercury are organic mercury compounds. Methylmercury has been extensively studied as a result of its accumulation in fish. For example, the FDA advises against consuming swordfish in order to reduce our exposure to mercury. In contrast, the CDC states that the amount of ethylmercury in vaccines is safe. The agency’s website covers the topic of thimerosal and ethylmercury in vaccines, yet lists just one published study from the past decade in support of the conclusions stated.
The CDC claims that ethylmercury in vaccines is “cleared from the body more quickly than methylmercury, and is therefore less likely to cause any harm” (1). This refers to the amount of ethylmercury in the blood after it’s injected via vaccine, based on the observation that the amount of ethylmercury in the blood drops more quickly than the same amount of methylmercury (9). Unfortunately this claim of safety is based on a lack of consideration for the toxicokinetics of injected ethylmercury and its transport, transformation, and (lack of) excretion from the body.
Burbacher et al. found by comparing methylmercury to thimerosal that while blood levels of ethylmercury post-injection drop more rapidly than blood levels of methylmercury post-ingestion, the percentage of inorganic mercury deposited in the brain after exposure to thimerosal was nearly five times higher than the amount of inorganic mercury deposited after methylmercury exposure. Therefore, it is not acceptable to use the safety profile of ingested methylmercury as a substitute for the injection of ethylmercury. There is not sufficient evidence for the CDC to conclude that the use of thimerosal in vaccines is safe.
Evidence of toxicity.
Over 165 scientific studies have been published on thimerosal and found it to be harmful (12). These studies have found that exposure to thimerosal has been associated with: neurotoxicity (13,14) and excitotoxic brain injury (15,16), lasting neuropathological changes (17), neurodevelopmental disorders and autism (14,16,18,19), immune system stimulation and inducing autoimmunity (20,21), kidney toxicity (22), modification of hormone levels (16), mitochondria toxicity (23), fetal toxicity (24,25,26), DNA damage (27), and more. When it comes to child development, thimerosal exposure has also been found to be a risk factor for tics, speech delay, language delay, neurodevelopmental delay, delayed startle response, decreased motor learning, and attention deficit disorder (12,25,26,28).
Current information regarding the toxicokinetics and toxicity of thimerosal does not support claims of safety for use in vaccines. Additionally, CDC’s claims are based on assumption rather than scientific data. Due to the nature of seasonal influenza vaccination, long-term experimental studies should be performed with repeated doses of thimerosal and a reference dose for ethylmercury based on injection, not ingestion, should be determined. Thimerosal-containing vaccines are administered to the most sensitive populations – infants, children, and the pregnant mothers of developing fetuses (11). With a dramatic increase in the incidence of neurodevelopmental disorders, it is warranted that exposure to known neurotoxicants during pregnancy, infancy, and childhood be critically examined.
1. CDC > Vaccine Safety > Thimerosal in Vaccines
2. FDA > Vaccines, Blood, & Biologics > Thimerosal in Vaccines
3. CDC > Morbidity and Mortality Weekly Report > Notice to Readers: Thimerosal in Vaccines: A Joint Statement of the American Academy of Pediatrics and the Public Health Service.
4. EPA > National Center for Environmental Assessment > Risk Assessment > Reference Dose for Methylmercury
5. Medscape > Influenza virus vaccine trivalent (Rx) > Dosing & Uses > Pediatric
6. CDC Immunization Schedules
7. CDC > Environmental Health Document > Mercury > 2009
8. Agency for Toxic Substances & Disease Registry (ATSDR) > Toxic Substances Portal – Mercury > Public Health Statement on Mercury, March 1999.
9. Neurotoxic character of thimerosal and the allometric extrapolation of adult clearance half-time to infants.
10. Comparison of blood and brain mercury levels in infant monkeys exposed to methylmercury or vaccines containing thimerosal.
11. EXTOXNET > Toxicology Information Brief > Dose-Response Relationships in Toxicology
12. Methodological issues and evidence of malfeasance in research purporting to show thimerosal in vaccines is safe.
13. Integrating experimental (in vitro and in vivo) neurotoxicity studies of low-dose thimerosal relevant to vaccines.
14. Transcriptomic analyses of neurotoxic effects in mouse brain after intermittent neonatal administration of thimerosal.
15. Administration of thimerosal to infant rats increases overflow of glutamate and aspartate in the prefrontal cortex: protective role of dehydroepiandrosterone sulfate.
16. A possible central mechanism in autism spectrum disorders, part 2: immunoexcitotoxicity.
17. Lasting neuropathological changes in rat brain after intermittent neonatal administration of thimerosal.
18. A dose-response relationship between organic mercury exposure from thimerosal-containing vaccines and neurodevelopmental disorders.
19. The biological basis of autism spectrum disorders: Understanding causation and treatment by clinical geneticists.
20. Immunosuppressive and autoimmune effects of thimerosal in mice.
21. Ethylmercury and Hg2+ induce the formation of neutrophil extracellular traps (NETs) by human neutrophil granulocytes.
22. A systematic study of the disposition and metabolism of mercury species in mice after exposure to low levels of thimerosal (ethylmercury).
23. Thimerosal-Derived Ethylmercury Is a Mitochondrial Toxin in Human Astrocytes: Possible Role of Fenton Chemistry in the Oxidation and Breakage of mtDNA
24. The effect of ethylmercury on fetal development and some essential metals levels in fetuses and pregnant female rats.
25. Low-dose mercury exposure in early life: relevance of thimerosal to fetuses, newborns and infants.
26. Maternal thimerosal exposure results in aberrant cerebellar oxidative stress, thyroid hormone metabolism, and motor behavior in rat pups; sex- and strain-dependent effects.
27. Thimerosal Induces DNA Breaks, Caspase-3 Activation, Membrane Damage, and Cell Death in Cultured Human Neurons and Fibroblasts.
28. Exposure to Mercury and Aluminum in Early Life: Developmental Vulnerability as a Modifying Factor in Neurologic and Immunologic Effects.