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Thimerosal exposure (from tetanus-diphtheria vaccine) during pregnancy and neurodevelopment of breastfed infants at 6 months


JG Dórea, C.P.04322, Universidade de Brasília, 70919-970, Brasília, DF, Brazil.
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Aim:  We studied the effect on neurodevelopment of infants who are exposed to thimerosal in tetanus-diphtheria (Td) vaccines during pregnancy.

Methods:  We compared Gesell Developmental Schedules (GDS) of exclusive breastfed infants at 6 months born to mothers who received Td (1 to 3 doses) against those who were born to mothers who did not take such vaccines.

Results:  Compared with the group of infants not exposed to ethylmercury in utero, the infants of exposed mothers showed no significant difference in neurodevelopment delays. Although there was a significant correlation between hair-Hg of mothers and hair-Hg of neonates (Spearman r = 0.353; p = 0.0011), there was no significant correlation between the level of in utero exposure to ethylmercury in Td vaccines and neonate’s hair-Hg concentrations (Spearman r = 0.060; p = 0.5922). However, regression analysis showed that GDS at 6 months was significantly associated with total mercury concentration of neonate’s hair but was not sensitive to the number of vaccines taken by the mother.

Conclusion:  Early neurodevelopment of exclusively breastfed infants is sensitive to in utero exposure to mercury, but maternal thimerosal exposure in tetanus-diphtheria vaccines per se cannot portend clinical neurodevelopment delays measured by GDS at 6 months.