New study shows that administration of vaccines containing thiomersal does not raise blood concentrations of mercury above safe levels in full-term infants
Published:
The study, which investigated the concentrations of mercury in the blood, urine and stools of full-term infants after the administration of routine childhood vaccines containing thiomersal, was published in November 2002. It found that the administration of these vaccines did not appear to raise blood concentrations of mercury above safe levels in infants and that thiomersal was eliminated rapidly from the body after vaccination. This provides reassurance about the safety of thiomersal as a preservative in childhood vaccines.
This study was carried out by Pichichero and colleagues in the USA and published in The Lancet Journal. The authors studied two groups of full-term infants (61 in total), one group who received thiomersal-containing vaccines and a second group who received thiomersal-free vaccines. The former group comprised 20 full-term infants aged 2 months and 20 aged 6 months and the latter comprised 21 infants. The study took place at routine vaccination visits in two centres in the USA between November 1999 and October 2000. The concentration of thiomersal in the infant's blood, urine and stools was examined at 3 to 28 days after vaccination.
Thiomersal remained in the blood of infants for only a short period of time (3 to 10 days) after vaccination indicating rapid excretion. The mean blood mercury in two month olds who received thiomersal-containing vaccines was 8.20 parts per billion (Range: 3.75 to 20.55 parts per billion). In 6 month olds who received thiomersal-containing vaccines, the mean blood mercury value was 5.15 parts per billion with all recorded values lower than 7.5 parts per billion. These blood concentrations of mercury are less than 29 parts per billion which is the concentration thought to be safe in umbilical cord blood when the foetus is in utero. Concentrations of mercury were low in the urine of infants who received thiomersal-containing vaccines but high in the stools indicating rapid excretion.
The study found that the amounts of mercury in the blood of infants receiving vaccines containing thiomersal are well below levels potentially associated with toxic effects. The authors concluded that thiomersal in routine vaccines poses very little risk to full-term infants.
