Second Opinion: MMR madness

As one of my colleagues gasped at the end of a gruelling session, being interrogated by parents armed with anti-vaccination propaganda produced by pressure groups (such as Jabs or The Informed Parent) - or gleaned from the internet - is like enduring an old-style exam viva. A father recently presented me with a substantial 'information pack' on MMR produced by a firm of solicitors which is leading the campaign for compensation for children allegedly damaged by the vaccine, including some 287 cases of autism.

The information pack is a fascinating and shocking document. One of its co-authors is introduced as having an 'encyclopaedic knowledge of medical matters' and even a BSc (Hons), clearly a prestigious qualification in legal circles. It opens rather defensively - 'we have ourselves been accused of being "ambulance chasers"' (no!) - and insists that the authors approach the subject, not only with 'an open mind', but with 'a completely open mind'. It then proceeds to the 'tentative conclusion', emphasising that 'our views are tentative', that if a child who was developing normally prior to receiving the MMR vaccine and subsequently became autistic, 'then in all probability the MMR vaccine has played a part in the cause of autism'. Not only is there virtually no evidence for this not very tentative conclusion, it is, as numerous commentators have pointed out, highly implausible.

Given the timing of the MMR immunisation - at around 15 months - it is not surprising that somebody should make a link with autism, which is usually diagnosed in the second year of life. But for this link to be established as one of caus-ation, rather than a mere association, further evidence is required.

If MMR really causes autism, one would expect an increase in cases following the introduction and mass implementation of the MMR vaccine (in 1988, reaching more than 90 per cent of the target population) and after the intensive MMR campaign in November 1994 (when some eight million children were immunised). This is straightforward for the lawyers, because 'anecdotal evidence suggests that there has been a huge rise in cases of childhood autism throughout the country'. They present a series of anecdotes and opinions - from the Norfolk Autistic Society, from the internet, from a National Autistic Society newsletter - but no hard data.

By contrast, for international author-ities in the field of autism (such as Lorna Wing in Britain and Christopher Gillberg in Sweden) the question of whether its prevalence is increasing is a difficult one to answer. Both acknowledge that it 'seems to be on the increase', but also point out problems of case definition, and improvements in the diagnosis of the condition. In a recent review of the literature, Wing concluded that there was 'no evidence for or against an increase in prevalence' (British Medical Journal, 312, 1996, pp327-8).

The case for MMR causing autism would be strengthened if, in individual cases, a clear relationship could be shown. But this is difficult because, while the MMR immunisation is a fixed event, the emergence of autism is, characteristically, an insidious process whose features become clear over months rather than weeks or days. The lawyers emphasise cases in which development proceeded normally into the second year, only to be followed by regression into autistic forms of behaviour. But it has long been recognised that while some cases of autism are apparent from early infancy, many only become apparent at 18 months or later. It is clear that nobody would suspect a link unless they were predisposed to suspect the harmful consequences of immunisation.

How is MMR supposed to cause autism? The information pack speculates about immunological reactions (with a reference to a GP free-sheet published in 1967). It further suggests that the vaccine promotes antibodies to myelin, the lining of nerve fibres (with references to research findings in obscure US journals which appear not to have been reproduced). In the paper about MMR, inflammatory bowel disease and autism that launched the scare back in April, Andrew Wakefield and his colleagues at the Royal Free Hospital in London cite the 'opioid excess' theory (Lancet, 351, 1998, pp637-41). They believe that toxins leak through an inflamed bowel wall into the blood stream, leading to the familiar neuro- psychiatric features. As an accompanying editorial points out, this theory does not well explain the fact that autistic behavioural features appear to predate the bowel inflammation which is supposed to release the toxins.

How is it that apparently open-minded people can endorse such absurd theories, and with such conviction? The legal information pack offers some clues.

In a revealing aside the authors warn that, in relation to the MMR-autism link, 'we have to proceed very carefully': 'There are many insults to the human body as a result of life in the last decade of the twentieth century. Pesticides, agricultural chemicals, antibiotics, preservatives, pollution or junk food may be responsible for the changing pattern of this serious and distressing childhood condition.' This litany of the fashionable preoccupations of the ecologically aware reveals an intense sense of personal vulnerability. But the selection of dangers is highly arbitrary: we might equally suggest that autism results from the exposure of babies to musical mobiles, bouncers and the Teletubbies.

In passing, the lawyers note that 'damage to children does not just happen'. 'There is always a cause', they continue, implying that somebody is always to blame - and therefore liable to pay compensation. One of the sobering aspects of working as a doctor is the realisation that damage does just happen - to children and adults - and in a bewildering variety of forms. To blame is human, but tilting at windmills is likely to prove a demoralising experience for everybody involved - except, of course, the lawyers.