Thiomersal
The GACVS considered the presentation of a recently published pharmacokinetic study of mercury in premature and low-birth-weight infants who received a birth dose of hepatitis B vaccine containing thiomersal.6 The results suggest that exposure to thiomersal-containing vaccines does not result in accumulation of mercury in blood and that the blood half-life (2.9–4.1 days) of intramuscular ethyl mercury from thiomersal in vaccines in infants is substantially shorter than that of oral methyl mercury in adults. The study concluded that exposure guidelines based on oral methyl mercury may not be appropriate for use in assessing the risk of thiomersal in vaccines at dosages consistent with standard vaccination regimens.
The GACVS also considered the results of a study conducted in Italy that examined the neuropsychological performance 10 years after immunization in infancy with thiomersal-containing vaccines (Tozzi A., unpublished data, 2008). According to the results, higher thiomersal exposure through vaccines administered in the first year of life was significantly associated with lower scores on 2 neuropsychological outcomes (motor function, measured using the finger-tapping test, and language, measured using the Boston naming test). The differences in mean scores were very small, detected only in girls, of doubtful clinical relevance, and not consistent with results from other studies of ethyl mercury. The observed associations may reflect the effect of chance.
On the basis of the presented data, GACVS remains of the view that there is no evidence supporting any change in WHO’s recommendations for thiomersal-containing vaccines and the vaccination of low-birth-weight infants where indicated.