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A cross-sectional study of the relationship between infant Thimerosal-containing hepatitis B vaccine exposure and
David A Geier1, Janet K Kern2, Kristin G Homme3
1Institute of Chronic Illnesses, Inc, Silver Spring, MD, USA; CoMeD, Inc., Silver Spring, MD, USA.
Insights
Infant exposure to Thimerosal-containing hepatitis B vaccine (T-HepB) was linked to a higher risk of attention-deficit/hyperactivity disorder (ADHD) diagnosis. While not proving causation, findings suggest a need to eliminate Thimerosal in vaccines.
Area of Science:
- Neurodevelopmental disorders
- Vaccine safety and epidemiology
- Public health research
Background:
- Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder affecting functioning in multiple settings.
- Thimerosal, a mercury-based preservative, was historically used in some vaccines, including hepatitis B vaccine (T-HepB).
- Concerns exist regarding potential links between Thimerosal exposure and neurodevelopmental outcomes in children.
Purpose of the Study:
- To evaluate the hypothesis that infant exposure to Thimerosal-containing hepatitis B vaccine (T-HepB) increases the risk of an ADHD diagnosis.
- To analyze the association between T-HepB exposure and ADHD diagnosis using a large, nationally representative dataset.
Main Methods:
- Cross-sectional study of 4393 individuals aged 13-19 years using combined 1999-2004 National Health and Nutritional Examination Survey (NHANES) data.
- Analysis of demographic, immunization, socioeconomic, and health-related variables.
- Statistical modeling including logistic regression, linear regression, Spearman's rank, and 2x2 contingency tables to assess the T-HepB and ADHD association, controlling for covariates.
Main Results:
- Three doses of T-HepB exposure were significantly associated with an increased risk of ADHD diagnosis compared to no exposure (adjusted odds ratio=1.980).
- Statistical models consistently indicated a positive association between T-HepB exposure and ADHD diagnosis.
- Health outcomes not biologically linked to T-HepB showed no association, supporting the specificity of the observed link.
Conclusions:
- The study found a statistically significant association between infant T-HepB exposure and an increased risk of ADHD diagnosis.
- While results are biologically plausible and supported by prior research, the cross-sectional design precludes establishing a direct cause-effect relationship.
- Eliminating Thimerosal exposure from vaccines is recommended, particularly as it remains in use in developing countries.
Abstract:
Attention-deficit/hyperactivity disorder (ADHD) is characterized by a marked pattern of inattention and/or hyperactivity-impulsivity that is inconsistent with developmental level and interferes with normal functioning in at least two settings. This study evaluated the hypothesis that infant Thimerosal-containing hepatitis B vaccine (T-HepB) exposure would increase the risk of an ADHD diagnosis. This cross-sectional study examined 4393 persons between 13 and 19 years of age from the combined 1999-2004 National Health and Nutritional Examination Survey (NHANES) by analyzing demographic, immunization, socioeconomic, and health-related variables using the SAS system. Three doses of T-HepB exposure in comparison to no exposure significantly increased the risk of an ADHD diagnosis using logistic regression (adjusted odds ratio=1.980), linear regression (adjusted beta-coefficient=0.04747), Spearman's rank (Rho=0.04807), and 2×2 contingency table (rate ratio=1.8353) statistical modeling even when considering other covariates such as gender, race, and socioeconomic status. Current health status outcomes selected on an a priori basis to not be biologically plausibly linked to T-HepB exposure showed no relationship with T-HepB. The observed study results are biologically plausible and supported by numerous previous epidemiological studies, but because the NHANES data is collected on a cross-sectional basis, it is not possible to ascribe a direct cause-effect relationship between exposure to T-HepB and an ADHD diagnosis. During the decade from 1991 to 2001 that infants were routinely exposed to T-HepB in the United States (US), an estimated 1.3-2.5 million children were diagnosed with ADHD with excess lifetime costs estimated at US $350-$660 billion as a consequence of T-HepB. Although Thimerosal use in the HepB in the US has been discontinued, Thimerosal remains in the HepB in developing countries. Routine vaccination is an important public health tool to prevent infectious diseases, but every effort should be made to eliminate Thimerosal exposure.
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