Even though scientific research aims to uncover truths, sometimes findings aren’t always an accurate reflection of “the truth.” This could be the result of unintentional human errors, misguided methodologies, or the omission of important results. In the case of Thimerosal, an organic-mercury based compound that was used as a preservative in childhood vaccines, the truth about its health risks now seems obscured by new flawed studies.
Thimerosal gained attention in the United States after a wide array of research found a link between Thimerosal-containing vaccines (TCVs) administered during early childhood and a higher risk for developing neurodevelopmental disorders like autism. Though Thimerosal was subsequently recommended to be removed from all vaccines by the US Public Health Service and American Academy of Pediatrics in 1999, it can still be found in some flu vaccines, which are administered to many pregnant women, infants, and children each year in the United States.
The CDC argues that Thimerosal is in no way attributed to neurodevelopmental diseases like autism, despite the fact that a study conducted by the CDC itself found a nearly 8-fold increase in autism rates when infants received Thimerosal-containing vaccines. In total, there have been over 160 different studies that have found Thimerosal to be harmful.
So we wonder: is Thimerosal getting a fair trial?
One reason to doubt the fairness of the Thimerosal debate is the fact that the six papers the CDC cites as evidence that Thimerosal is safe were all conducted, funded, or cosponsored by the CDC itself. In his 2014 paper “Methodological Issues and Evidence of Malfeasance in Research Purporting to Show Thimerosal in Vaccines is Safe,” Dr. Mark Geier assesses each of the six studies that the CDC has used as proof there is no link between autism and TCVs.
What did Geier find?
- A paper published by Madsen et al. in 2003 argued that the rates of autism in Denmark actually increased when Thimerosal was removed from vaccines. However, the paper had a major flaw in its methodology. Researchers first calculated the number of those who had received TCVs and developed autism based on data collected solely from inpatient visits, yet then calculated the number of those with autism after TCVs were banned based on data from both inpatient and outpatient visits; this made it appear as if cases increased after TCVs were banned, when in fact the researchers simply looked at a larger pool of data.
- The CDC’s Stehr-Green et al. study in 2003 provides inaccurate information about TCVs because it compare the correlation of TCVs and autism between three different countries (the U.S., Sweden, and Denmark), without acknowledging the presence of influential factors like varying quantities of Thimerosal and a reliance on a small sample population.
- The Hviid et al. study, also conducted in 2003, states that populations that received TCVs were not at an increased risk of developing autism. However, the study’s sample population included children as young as 1 year of age, an age at which most are too young to start showing signs of autism. The study therefore could not accurately determine that actual number of children who received TCVs and developed autism.
- In 2004, the Andrews et al. study found that TCVs resulted in a lower risk for developing neurodevelopmental disorders, yet the study evaluated data from children that experienced significantly different vaccination schedules and were diagnosed based on different criteria. Further, all subjects were given the same follow up times; in other words, if the subject didn’t develop a disorder within a standard amount of time, no correlation was reported. However, we know that disorders can appear at any time in an individual’s life, which means that using a standard follow up time is ineffective. This research is also based on subjects from the UK who received lower quantities of Thimerosal in TCVs than children did in the U.S.
- The CDC’s 2003 Verstraeten et al. study stated there was no relationship between Thimerosal and cases of autism after studying data from the Vaccine Safety Datalink, yet the paper (which only published findings on the fifth of the study’s five phases) inexplicably did not include any actual data to back this claim. Interestingly, the first phase of the study (which was only published internally), found that infants who were exposed to more than 25 micrograms of Mercury were 7.6 times more likely to develop autism. The following phases of the study employed manipulative methodologies that were able to drop this figure to just 1.69.
- 2010’s Price study found that pre-natal and infant exposure to TCVs presented no significant risk for developing autism. Yet, this conclusion was based on a matching methodology that resulted in flaw known as overmatching, as matching variables were in fact significant predictors of exposure. Further, the study also did not report that it found that prenatal exposure to Thimerosal resulted in an 8.73 increase in risk for regressive autism.
Each of the six primary studies the CDC cites as evidence that Thimerosal doesn’t increase the risk for autism have significant flaws in methodology and reporting. Therefore, it seems that if the debate about Thimerosal is to be fair, research cited to support arguments should at the very least be founded on sound approaches.