The Evidence
The Centre for Disease Control has funded extensive research into this topic, specifically on a component used as a preservative in vaccines.
Thimerosal, the mercury-based preservative in vaccinations, has been under fire due to its safety concerns. Since 2003, there was numerous thimerosal-related studies that were conducted by the CDC or with the CDC’s involvement to study the implications of vaccines on human development (CDC, 2015).
A few of the major studies are highlighted below.
Effects of thimerosal on brain function, behavior, language, coordination
In this study, thimerosal exposure in early life was assessed and correlated with seven specific neuropsychological outcomes in 7-10-year-old children. According to the study, there was no associations with thimerosal and general intellectual functioning, executive functioning, fine motor coordination, verbal memory, behavior regulation and language. There was a small but insignificant association between early thimerosal exposure and the presence of tics in boys, however, this was not observed in girls (Barile et al., 2012)
Effects of thimerosal exposure in the womb and in infancy
In a study, thimerosal has been hypnotized to be associated with an increased risk of Autism Spectrum Disorder (ASD). Prenatal and infant exposure to thimerosal was assessed as well as exposure to thimerosal in children with Autism compared to those without. The study found no differences in exposure to thimerosal between children with and without Autism (Prince et al., 2010).
Another CDC conducted study showed there was no increased risk of developing Autism from exposure to the components that elicit an immune response in vaccines during the first 2 years of life (Destefano, Price and Weintraub, 2014).
Thimerosal and Children’s Flu Shots
As a recommendation, Flu shots are advised annually which marks the concern for its involvement in the risk of ASD. This study measured the proportion of injection site reactions (ISR), rashes, and infections that were reported after vaccination. Three versions of an inactivated influenza vaccine (IIV), including thimerosal-free, thimerosal-including, and ones in which the presence of thimerosal could not be determined, was tested in children less than 2 years of age. The study concluded that there was no difference in the proportion of ISR, rashes, and infections in all three versions of IIV which suggests that thimerosal is not a harmful preservative (McMahon et al., 2008)
Long-term results of thimerosal exposure
This study compared the long-term neuropsychological outcomes for children who were randomly assigned to receive one of two forms of diphtheria-tetanus acellular pertussis vaccine (DTaP) in the first year of their life; one of these forms containing thimerosal and the other containing 2-phenoxyethanol. Ten years after vaccination, 24 neuropsychological outcomes were assessed in the children. The results have shown that only two of the 24 outcomes are associated with thimerosal exposure, but this may have been due to chance. Ultimately it is concluded that thimerosal exposure is not harmful in children (Tozzi et al., 2009).
Comparing outcomes with and without thimerosal
In 1992, Denmark and Sweden terminated the use of thimerosal in vaccinations. In contrast, thimerosal dose in the United Stated increased in the 1990s. This study done at the University of Washington compares the rate of Autism in these countries before and after thimerosal was removed. The study has found that in all three countries, the incidence and prevalence of autism-like disorders began to rise in the 1985-1989 period, and the rate of increase accelerated in the early 1990s. With the removal of thimerosal by Denmark and Sweden, the acceleration in the prevalence of Autism cannot be attributed to thimerosal (Stehr-Green et al., 2003).
A meta-analysis (review of research) was conducted on case control and cohort studies to summarize available evidence. With five cohort studies and five case control studies, over 1.2 million children and a two reviewer analysis, no relationship between vaccination and autism was found (Taylor, Swerdfeger and Eslick, 2014). No relationship was found between the MMR vaccine, thimerosal or mercury for the risk of developing autism spectrum disorder (Taylor, Swerdfeger and Eslick, 2014).
Further research by the CDC stated that “the evidence favours rejection of a causal relationship between thimerosal-containing vaccines and autism” (CDC, 2015).
With overwhelming evidence against a correlation between vaccines and autism, the question remains where does the vaccine and anti-vaccine movement come from? See below for answers!
Sources:
Barile, J. P., Kuperminc, G. P., Weintraub, E. S., Mink, J.W., & Thompson, W. W. (2012). Thimerosal exposure in early life and neuropsychological outcomes 7-10 years later. Journal of Pediatric Psychology, 37(1), 106–118.
CDC. (2015, October 27) Vaccines Do Not Cause Autism Concerns. Centers for Disease Control and Prevention. Center for Disease Control and Prevention.
Destefano, F., Price, C. S., and Weintraub, E. S. (2014) Increasing Exposure to Antibody-Stimulating Proteins and Polysaccharides in Vaccines Is Not Associated with Risk of Autism. Journal of Pediatrics 89.
McMahon, A. W., Iskander, J. K., Haber, P., Braun, M. M., & Ball, R. (2008). Inactivated influenza vaccine (IIV) in children <2 years of age: examination of selected adverse events reported to the Vaccine Adverse Event Reporting System (VAERS) after thimerosal-free or thimerosal-containing vaccine. Vaccine, 26(3), 427–429.
NCEZID. (2015, November 23) CDC Studies on Thimerosal in Vaccines. Vaccine Safety. Center for Disease Control.
Price, C. S., Thompson, W. W., Goodson, B., Weintraub, E. S., Croen, L. A., Hinrichsen, V. L., … DeStefano, F. (2010). Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism. Pediatrics, 126(4), 656–664.
Stehr-Green, P., Tull, P., Stellfeld, M., Mortenson, P.-B., & Simpson, D. (2003). Autism and thimerosal-containing vaccines: lack of consistent evidence for an association. American Journal of Preventive Medicine, 25(2), 101–106.
Taylor, L. E., Swerdfeger, A. L., and Eslick, G. D. (2014) Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies. Pub-Med 32, 3623–3629.
Tozzi, A. E., Bisiacchi, P., Tarantino, V., De Mei, B., D’Elia, L., Chiarotti, F., & Salmaso, S. (2009). Neuropsychological performance 10 years after immunization in infancy with thimerosal-containing vaccines. Pediatrics, 123(2), 475–482.