Thursday, October 20, 2005

Autism Spectrum Disorder and vaccine studies

SCIENTISTS have strongly rejected any suggestion that the measles, mumps and rubella vaccine, MMR, is linked to disorders such as autism.
An analysis of 31 MMR studies by the Cochrane Library, the most authoritative source of evidence-based medicine, has shown no credible grounds for claims of serious harm.

Uptake of the vaccine decreased sharply after research by Andrew Wakefield, published in The Lancet in 1998, suggested a direct causal link between autism and Crohn’s disease. The research, since discredited, resulted in the uptake falling to less than 70 per cent in some parts of Britain — far below the 95 per cent recommended by the World Health Organisation. This has been blamed for contributing to an increase in measles and mumps.
Health campaigners hope that the latest analysis, published in the Cochrane Review, will boost the MMR uptake. It supports a study published in The Lancet last year that poured scorn on the suggestion of a link between the combined vaccine and autism.
The conclusions of the Cochrane Library — a collection of evidence-based medicine databases — draw together all the available information from around the world. Vittorio Demicheli, the lead author, said: “We conclude that all the major unintended events, such as triggering Crohn’s disease or autism, were suspected on the basis of unreliable evidence.”
MMR uptake has improved in Britain, but remains worryingly low in some areas after the coverage of the negative research. Statistics from the Health and Social Care Information Centre showed that uptake among two-year-olds in England was 81 per cent in 2004-05 — up from 80 per cent in 2003-04. This was the first year-on-year increase since 1995-96, when uptake peaked at 92 per cent.
In 1997 there were 117 cases of measles but in 2002 there were more than 300. Dr Demicheli said: “Public health decisions need to be based on sound evidence. If this principle had been applied, we would have avoided all the fuss.”
The MMR vaccine was introduced in the US during the 1970s and is used in more than 90 countries. The Cochrane systematic review said that MMR was an important vaccine that had “prevented diseases that still carry a heavy burden of death and complications where the vaccine is not used”.
MMR was introduced in Britain in 1988
Children are given a first dose of the MMR jab at 12 to 15 months and a booster dose at between three and five years old
One MMR jab can prevent measles infection in 90 per cent of all immunised children. A second dose raises this level of protection from measles to 99 per cent
About 2,000 families in Britain have taken legal action claiming their children have been damaged by the MMR jab, with many believing it has triggered autism