OBJECTIVE. Thimerosal, a mercury compound used as a preservative in vaccines administered during infancy, has been suspected to affect neuropsychological development. We compared the neuropsychological performance, 10 years after vaccination, of 2 groups of children exposed randomly to different amounts of thimerosal through immunization.
METHODS. Children who were enrolled in an efficacy trial of pertussis vaccines in 1992–1993 were contacted in 2003. Two groups of children were identified, according to thimerosal content in vaccines assigned randomly in the first year of life (cumulative ethylmercury intake of 62.5 or 137.5 μg), and were compared with respect to neuropsychological outcomes. Eleven standardized neuropsychological tests, for a total of 24 outcomes, were administered to children during school hours. Mean scores of neuropsychological tests in the domains of memory and learning, attention, executive functions, visuospatial functions, language, and motor skills were compared according to thimerosal exposure and gender. Standard regression coefficients obtained through multivariate linear regression analyses were used as a measure of effect.
RESULTS. Nearly 70% of the invited subjects participated in the neuropsychological assessment (N = 1403). Among the 24 neuropsychological outcomes that were evaluated, only 2 were significantly associated with thimerosal exposure. Girls with higher thimerosal intake had lower mean scores in the finger-tapping test with the dominant hand and in the Boston Naming Test.
CONCLUSIONS. Given the large number of statistical comparisons performed, the few associations found between thimerosal exposure and neuropsychological development might be attributable to chance. The associations found, although statistically significant, were based on small differences in mean test scores, and their clinical relevance remains to be determined.
Comments
This study is not methodologically correct
The study by Tozzi and others has many limitations.
No comparison is done with children not exposed to thimerosal and neuropsychological disturbances are studied in recruiting voluntary all children even healthy ones, without assessing the sensitivity individual mercury.
With this background this study can not lead to any conclusion.
It is possible to evaluate the role of vaccines and thimerosal in neurodevelopmental disorders with the study of immune response. In my case I found a hyperimmune response to measles, polio with autoimmune reaction against myelin and glia. Moreover, the presence of antifibrillarin antibodies indicates an autoimmune response induced by mercury (HgIA).
All this can not be a coincidence.
Conflict of Interest:
doctor and father of a child with neurodevelopmental disorder
What are the Italians Doing Right?
In the article, "Neuropsychological Performance 10 Years After Immunization in Infancy With Thimerosal-Containing Vaccines", the authors identify only 1 case of autism among 1,704 subjects who were involved in the study. That makes for some real simple math, 1:1704. The rate of autism in the U.S. is 1:150. What are the Italians doing right? Why are their autism rates more than 10 times lower?
Conflict of Interest:
Father of an autistic child
This study is misleading and was not scientifically worth doing
I note the conclusion of this study by Tozzi, Bisiacchi, Tarantino, De Mei, D'Elia, Chiarotti and Salmaso [1]. However, I also note the limitations of the study as described in the discussion:
'Some limitations should be considered in the interpretation of our results. The cumulative intake of thimerosal was relatively low, compared with that in other countries including the United States, where vaccination schedules included more thimerosal-containing vaccines in the first year of life. Moreover, there was no comparison group with no exposure to thimerosal, although our setting was appropriate to identify a dose response effect in the absence of any evidence suggesting a threshold dose for observation of an effect. Our analysis included only healthy children who were selected during enrollment in the original trial, and some families might have declined to participate in the present study because their children had cognitive developmental problems. This might have reduced the prevalence of adverse neuropsychological conditions and might have made potential differences hard to detect. The eligibility criteria of the original trial also limited the participation of low birth weight children, and only 55 children with birth weights of <2500 g underwent the neuropsychological evaluation (data not shown). Moreover, only 1% of children in this study received hepatitis B virus vaccine at birth. Although no effect of birth weight according to thimerosal intake was detected through multivariate analyses, our study was not powered to detect an association of thimerosal exposure and neuropsychological development in low birth weight infants.' [1]
I ask how it would be possible to draw any useful scientific conclusions from a study with such deficiencies in relation to the issues it purportedly set out to investigate? But I also reflect on the headline value of negative results for wider media consumption, as in the Associated Press report by Carla K Johnson, with contributions from Alberto Tozzi himself, Jennifer Pinto-Martin and Paul Offit [2] claiming this strengthens the evidence base for vaccine safety.
[1] Alberto Eugenio Tozzi, Patrizia Bisiacchi, Vincenza Tarantino, Barbara De Mei, Lidia D'Elia, Flavia Chiarotti, and Stefania Salmaso, 'Neuropsychological Performance 10 Years After Immunization in Infancy With Thimerosal-Containing Vaccines', Pediatrics 2009; 123: 475-482.
[2] Carla K Johnson, 'Study adds to evidence of vaccine safety', Associated Press, http://www.google.com/hostednews/ap/article/ALeqM5jp7ZD1RFVm7yOzgaB04Ra4dY_ZuQD95UKPPG0
Conflict of Interest:
Parent of an autistic son