Vaccine
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While a number of studies remain to be completed, evidence is mounting that there is no demonstrable risk for infants immunized with vaccines containing thiomersal. Epidemiological studies in the US have shown no developmental or other central nervous system abnormalities resulting from exposure to vaccines containing thiomersal. During the initial evaluation of thiomersal in vaccines during 1999, the toxicological profile of ethyl mercury was unknown and presumed to be the same as that of methyl mercury. ⋯ Until such time as the scientific evidence is to hand, thiomersal-free presentations of hepatitis B are to be preferred for the birth dose. Given the same levels of exposure, adults are at much lower levels of risk because of increased body mass. It is not possible to prove that thiomersal is completely safe-epidemiology can only quantify a risk, not prove its absence.