Why thimerosal was removed from vaccines in the early 2000s
I recently wrote an entry which sparked a mini-war in the comments between myself and, what appears to be an anti-vaccine proponent. Many arguments were discussed, a few barbs were exchanged, and inevitably the topic of thimerosal came up. The commenter claimed that thimerosal was removed by the authorities “based on scientific analysis”. My reply was the standard: thimerosal was removed as a precautionary measure, in response to public outcry, stirred on by the anti-vaccine movement and their fear-mongering that mercury in vaccines was causing autism. The commenter replied to this:
No, you need to buff up on your history. Thimerosal was investigated because the government and EPA identified the danger of mercury exposure to the population at large and ordered an analysis into every exposure. The FDA then realized that exposures were occurring through Thimerosal and since mercury is a potent neurotoxin (that’s why the analysis was ordered in the first place) and that exposures were causing problems in the population, that it was prudent to eliminate that route of exposure. You seem to be falling for some manufactured history here.
Could it be that my understanding of the history of thimerosal is wrong? It is certainly possible, after all we all know how unreliable memory can be and how we humans can remember things wrong. So I decided to look it up, as a refresher, and to ensure that my comment was in fact correct. The CDC thankfully has a general timeline of the thimerosal saga. So let us go through it and see if the authorities did in fact remove thimerosal because they realized that mercury exposure “was occurring through Thimerosal”, or they removed it as a precaution.
Thimerosal Saga Timeline
07/07-1999 - The American Academy of Pediatrics and the Public Health Service issue a joint statement that says “there is no data or evidence of any harm caused by the level of exposure that some children may have encountered in following the existing immunization schedule. Infants and children who have received thimerosal-containing vaccines do not need to be tested for mercury exposure.“ Furthermore it states (emphasis added):
The recognition that some children could be exposed to a cumulative level of mercury over the first 6 months of life that exceeds one of the federal guidelines on methyl mercury now requires a weighing of two different types of risks when vaccinating infants. On the one hand, there is the known serious risk of diseases and deaths caused by failure to immunize our infants against vaccine-preventable infectious diseases; on the other, there is the unknown and probably much smaller risk, if any, of neurodevelopmental effects posed by exposure to thimerosal. The large risks of not vaccinating children far outweigh the unknown and probably much smaller risk, if any, of cumulative exposure to thimerosal-containing vaccines over the first 6 months of life.
Nevertheless, because any potential risk is of concern, the Public Health Service (PHS), the American Academy of Pediatrics (AAP), and vaccine manufacturers agree that thimerosal-containing vaccines should be removed as soon as possible. Similar conclusions were reached this year in a meeting attended by European regulatory agencies, European vaccine manufacturers, and FDA, which examined the use of thimerosal-containing vaccines produced or sold in European countries.
So, what the CDC and the American Academy of Pediatrics were saying on 07/07/1999 is that there is no known risk from exposure to thimerosal, but regardless they were moving to have it removed regardless of this lack of evidence, solely based on “potential risk”. This seems to support my claim that thimerosal was removed out of precaution, not evidence of harm.
11/05/1999 – CDC states that vaccine manufacturers, FDA, and other agencies are working together to reduce the amount of thimerosal in vaccines, or to replace them with thimerosal-free vaccines, as soon as possible. It stated the following (emphasis added):
The risk, if any, to infants from exposure to thimerosal is believed to be slight. The demonstrated risks for not vaccinating children far outweigh the theoretical risk for exposure to thimerosal-containing vaccines during the first 6 months of life.
Given the availability of vaccines that do not contain thimerosal as a preservative, the progress in developing such additional vaccines, and the absence of any recognized harm from exposure to thimerosal in vaccines, hepatitis B, DTaP, and Hib vaccines that contain thimerosal as a preservative can continue to be used in the routine infant schedule beginning at age 2 months along with monovalent or combination vaccines that do not contain thimerosal as a preservative.
1999 – From the CDC website (emphasis added):
The FDA reviews the use of thimerosal in childhood vaccines and finds no evidence of harm, but as a precautionary measure, recommends removing thimerosal from vaccines routinely given to infants.
05/05/2001 – A risk assessment of thimerosal use in childhood vaccines, published in the journal Pediatrics, finds no evidence of harm from the use of thimerosal as a preservative, other than redness and swelling at the injection site. More specifically the authors concluded as such (emphasis added):
Conclusion. Our review revealed no evidence of harm caused by doses of thimerosal in vaccines, except for local hypersensitivity reactions. However, some infants may be exposed to cumulative levels of mercury during the first 6 months of life that exceed EPA recommendations. Exposure of infants to mercury in vaccines can be reduced or eliminated by using products formulated without thimerosal as a preservative.
10/01/2001 - IOM’s Immunization Safety Review Committee issues a report concluding there is not enough evidence to disprove claims that thimerosal in childhood vaccines causes autism, attention deficit hypersensitivity disorder, or speech or language delay. This is yet another better safe than sorry kind of report; there is no evidence that it is harmful, but we can’t prove it isn’t either.
2001 – Except for influenza (flu), thimerosal is removed from or reduced in all vaccines routinely recommended for children 6 years of age and under manufactured for the U.S. market.
08/2003 – A study looks for a link between autism incidence and the use of thimerosal-containing vaccines. The study does not find a link between thimerosal-containing vaccines and autism in Denmark and Sweden, where autism rates continued to increase although thimerosal was removed from vaccines in 1992. Study authors conclude as such (emphasis added):
CONCLUSIONS: The body of existing data, including the ecologic data presented herein, is not consistent with the hypothesis that increased exposure to Thimerosal-containing vaccines is responsible for the apparent increase in the rates of autism in young children being observed worldwide.
11/2003 - Another study, published in Pediatrics, finds no consistent significant associations between exposure to thimerosal-containing vaccines and a variety of kidney, nervous system, and developmental problems. The authors concluded as follow (emphasis added, TCV means Thimerosal-Containing Vaccines):
Conclusions. No consistent significant associations were found between TCVs and neurodevelopmental outcomes. Conflicting results were found at different HMOs for certain outcomes. For resolving the conflicting findings, studies with uniform neurodevelopmental assessments of children with a range of cumulative thimerosal exposures are needed.
05/17/2004 - After reviewing scientific studies that examined thimerosal-containing vaccines and autism, the Institute of Medicine, IOM, concludes in a report that the studies “consistently provided evidence of no association between thimerosal-containing vaccines and autism.”
07/07/2007 – CDC issues a statement on autism and thimerosal that states in part “Some people believe increased exposure to thimerosal (from the addition of important vaccines recommended for children) explains the higher prevalence [of autism] in recent years. However, evidence from several studies examining trends in vaccine use and changes in autism frequency does not support such an association.“
09/27/2007 – A CDC study does not support an association between early exposure to thimerosal in vaccines and nervous system disorders in children between the ages of 7 and 10 years.
The weight of the evidence in this study does not support a causal association between early mercury exposure from thimerosal-containing vaccines and/or immunoglobulins and neuropsychological functioning at ages 7 to 10 years.
09/13/2010 – Another CDC study, published in Pediatrics, shows no connection between prenatal and infant exposure to thimerosal and autism rates. The authors concluded as such (emphasis added):
CONCLUSIONS In our study of MCO members, prenatal and early-life exposure to ethylmercury from thimerosal-containing vaccines and immunoglobulin preparations was not related to increased risk of ASDs.
First, let us bear in mind that this entry’s goal is not to summarize all the evidence, or lack there off, about thimerosal and its safety, but the goal was to verify my comment in the exchange with the commenter that the authorities decided to remove thimerosal not because of the scientific evidence showing harm, as the commenter claimed, but as a precautionary method.
All the documents linked to above point in the same direction; each one reaches the conclusion that there was no evidence of risk from thimerosal in vaccines. All risks are hypothetical, and since these studies could never prove definitively that thimerosal in vaccines doesn’t cause any extremely rare serious, they’re all couched in the “maybe” language. They all read as follows: No evidence of harm was found, but we can’t prove it so let’s take it out just to be safe. This is being interpreted by the anti-vaccine crowd as the “authorities admitting that the scientific evidence shows that thimerosal is harmful”.
I am the one who is being told to re-learn the history, but based on this evidence I’ve presented here today, it appears it is some on the anti-vaccine crowd that either do not know, or willfully misinterpret, the history.