Safety of thimerosal-containing vaccines: a two-phased study of computerized health maintenance organization databases.
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.
Epidemic Intelligence Service Program, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
Thomas
T
Verstraeten
Robert L
RL
Davis
Frank
F
DeStefano
Tracy A
TA
Lieu
Philip H
PH
Rhodes
Steven B
SB
Black
Henry
H
Shinefield
Robert T
RT
Chen
D015331:Cohort Studies; D016208:Databases, Factual; D002658:Developmental Disabilities / Q000139:chemically induced* / Q000453:epidemiology; D005260:Female; D006279:Health Maintenance Organizations / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011310:Preservatives, Pharmaceutical / Q000009:adverse effects*; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012306:Risk; D012449:Safety; D013849:Thimerosal / Q000009:adverse effects*; D014612:Vaccines
D011310:Preservatives, Pharmaceutical; D014612:Vaccines; D013849:Thimerosal