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Safety of thimerosal-containing vaccines: a two-phased study of computerized health maintenance organization
Thomas Verstraeten1, Robert L Davis, Frank DeStefano
1Epidemic Intelligence Service Program, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
Insights
This study found no consistent links between thimerosal-containing vaccines (TCVs) and infant neurodevelopmental disorders. Some conflicting results emerged across different health organizations, highlighting the need for further research.
Area of Science:
- Pediatric Health
- Neurodevelopmental Disorders
- Vaccine Safety
Background:
- Thimerosal, a mercury-based preservative, has been used in vaccines.
- Concerns exist regarding potential neurodevelopmental toxicity of thimerosal-containing vaccines (TCVs) in infants.
Purpose of the Study:
- To assess the potential toxicity of thimerosal-containing vaccines (TCVs) on infant neurodevelopmental outcomes.
- Investigate associations between mercury exposure from TCVs and neurodevelopmental disorders.
Main Methods:
- A two-phased retrospective cohort study utilized health maintenance organization (HMO) databases.
- Analyzed data from over 140,000 infants across multiple HMOs, calculating relative risks for neurodevelopmental disorders based on cumulative mercury exposure from TCVs.
Main Results:
- Phase I showed a positive association between TCV exposure and tics at 3 months in one HMO, and language delay at 3 and 7 months in another.
- Phase II found no significant associations for any neurodevelopmental outcomes.
- No significant increased risks for autism or attention-deficit disorder were observed in any analysis.
Conclusions:
- No consistent significant associations were found between TCVs and neurodevelopmental outcomes across the study.
- Conflicting results between different HMOs indicate variability in findings.
- Further research with standardized neurodevelopmental assessments is needed to resolve discrepancies.
Objective:
To assess the possible toxicity of thimerosal-containing vaccines (TCVs) among infants.
Methods:
A 2-phased retrospective cohort study was conducted using computerized health maintenance organization (HMO) databases. Phase I screened for associations between neurodevelopmental disorders and thimerosal exposure among 124 170 infants who were born during 1992 to 1999 at 2 HMOs (A and B). In phase II, the most common disorders associated with exposure in phase I were reevaluated among 16 717 children who were born during 1991 to 1997 in another HMO (C). Relative risks for neurodevelopmental disorders were calculated per increase of 12.5 micro g of estimated cumulative mercury exposure from TCVs in the first, third, and seventh months of life.
Results:
In phase I at HMO A, cumulative exposure at 3 months resulted in a significant positive association with tics (relative risk [RR]: 1.89; 95% confidence interval [CI]: 1.05-3.38). At HMO B, increased risks of language delay were found for cumulative exposure at 3 months (RR: 1.13; 95% CI: 1.01-1.27) and 7 months (RR: 1.07; 95% CI: 1.01-1.13). In phase II at HMO C, no significant associations were found. In no analyses were significant increased risks found for autism or attention-deficit disorder.
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.
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