Much publicity has been given to those who advocate that the MMR vaccine is the cause of the rising numbers of children being diagnosed as having an autistic spectrum disorder. This MMR scare began in 1998 with a study by Dr Wakefield et al published in the Lancet. The study has since been widely discred-ited and no valid scientific evidence has ever been produced to support such a hypothesis. On the contrary, a large number of rigorous scientific studies have testified to the vaccine's safety and absence of linkage with autism. The MMR vaccine does not contain thiomersal.

Having failed to demonstrate the culpability of the MMR vaccine, we are now being told that it is thiomersal, a preservative present in a certain brand of the Diphtheria/Pertussis/ Tetanus vaccine (DTP), that is the cause of the perceived rise in autism in recent years. Better diagnosis and changes in diagnostic classification are often ignored as at least part of the explanation for the rise. This assertion is strange in the context that DTP vaccine has been in use for over 60 years and yet this claimed "epidemic of autism" is a relatively new phenomenon. In addition it is also the case that the amounts of thiomersal received by children from the infant immunisation programme in the UK have decreased in recent times. These facts clearly contradict a causal relationship between thiomersal and recent rises in autism.

Almost all previous studies on the toxicological effects of heavy metals such as mercury and lead have substantiated a positive correlation between very high levels of these substances found in hair and an increasing adverse effect on neuro-logical development. Whereas in this quoted study the amount of mercury found in the hair of autistic children is less than in the non-autistic children. Yet somehow it is hypothesised, without any evidence, that mercury build- up somewhere else in the body is responsible for their autistic symptoms.

Finally, it is the view of this department that such unsubstantiated and ill-founded claims are detrimental to public confidence in the childhood vaccination programme. This programme has been an outstanding success in eradicating serious and life- threatening infections in recent times. Irresponsible scaremongering could eventually result in death and serious disability in many children if these diseases are allowed to return due to low vaccine- uptake.

It is also a cruel blow to all those parents of autistic children who are now being erroneously informed that they have permanently damaged their own children because of their responsible actions in attempting to protect their loved ones against the consequences of contracting such diseases.

Vincent McKeown, public health nurse; Dr Syed Ahmed, immunisation co-ordinator, Public Health, Greater Glasgow NHS Board, 350 St Vincent Street, Glasgow.