A new study of children’s behaviour problems has come to the conclusion that there is no discernible link with the three-in-one vaccine now being phased out in the UK.
Researchers from the University of Bristol’s Children of the 90s project – also known as the Avon Longitudinal Study of Parents and Children (ALSPAC) had been asked to investigate the DTP jab which, until now, has been routinely given to UK babies from the age of two months to protect against diphtheria, tetanus and whooping cough.
But after going through the immunisation records of almost 13 thousand children – they found no evidence linking it to developmental disorders.
Their report is one of two parallel studies* published today (September 7) in the journal Pediatrics which appear to support the use of the mercury-based thiomersal as a preservative in vaccines.
The children involved in the Bristol study were born at a time when the DTP vaccination schedule was brought forward to 2, 3 and 4 months of age (compared with previous recommendations of 3, 5 and 10 months). ALSPAC was asked to investigate whether the earlier exposure was associated with any adverse reactions.
In the UK, the vaccine contains thiomersal, (also known as thimerosal) a preservative containing ethyl mercury which has been used in medicines since the 1930s.
The preservative is being phased out in some countries in an effort to reduce overall exposure to mercury in any form. The Department of Health announced last month (August) that in future babies would receive a new five in one vaccine, which does not contain thiomersal.
There has been speculation that thiomersal could affect a child’s brain development although the Department of Health has always said there is no evidence of such a link.
The Bristol researchers went back through the immunisation records of 12,956 children to determine their mercury intake by the age of six months and then compared it with information on each child from birth to the age of 7½.
In all, the researchers looked at 23 different measures of the child’s behaviour and development – from emotional symptoms to hyperactivity, conduct problems, difficulties with speech, fine motor skills, tics, social skills and special educational needs.
Contrary to expectation, the figures appeared to show that the earlier the child was immunised – the fewer problems that were reported as they got older. Even after adjusting for other factors such as birthweight and whether the child was breastfed, the effect appeared to be beneficial.
The report concludes: “We could find no convincing evidence that early exposure to thiomersal had any deleterious effect on neurological or psychological outcome.
“This is particularly reassuring for developing countries receiving DTP vaccines and where multi-dose vials containing thiomersal as a preservative are often the only option.
“In the face of this evidence, we would support the view that the dangers posed by contaminated vaccine vials far outweigh any potential risk posed by thiomersal.”
Thiomersal exposure in infants and developmental disorders: A prospective cohort study in the United Kingdom does not support a causal association. Jon Heron, Jean Golding, and the ALSPAC Study Team. Pediatrics September 2004.
Speculation over the safety of thiomersal stems from studies of another related organic compound, methyl mercury (MeHg), which has been shown to be toxic in large quantities. There is also evidence that lower doses of Methyl mercury can affect childhood development in the womb or in the early months of life. Thiomersal contains a different form of mercury (ethyl mercury) which is metabolized and removed from the body much faster.
ALSPAC The Avon Longitudinal Study of Parents and Children (also known as Children of the 90s) is a unique ongoing research project based in the University of Bristol. It enrolled 14,000 mothers during pregnancy in 1991-2 and has followed the children and parents in minute detail ever since.