Guest editorial: MMR and autism
In this guest article, Science Writer Michael Marshall discusses the controversy surrounding the multiple vaccine for measles, mumps, and rubella, the so-called MMR vaccine.
UPDATE - a new statistical analysis of the risk factors associated with MMR and the diseases it seeks to prevent was published in the Sciencebase Science Blog by David Bradley on September 7, 2007 under the title MMR and Statistical Lies.
MMR: Are the Scaremongers Right? by
Over the course of the past two months, 38 students at Cambridge University in England were diagnosed with the contagious viral disease mumps, which affects the glands and causes fever. This is a colossal rise from the previous average of just one or two cases each year. Other universities are reporting a similar increase in incidence.
Many of the current generation of university students were not immunised against mumps. They were born several years too early to receive the combined MMR (mumps, measles and rubella) childhood vaccination, which has only been available since 1988. University authorities across England are now urging all students to obtain the MMR jab if they have not already done so.
The situation is a stark illustration of the consequences of failure to vaccinate. A disease that had been virtually non-existent within the population has made a sudden comeback. While mumps is generally harmless, it can in rare cases be fatal and can cause severe complications, such as sterility in men.
Given this situation, the University's decision to urge students to obtain MMR seems pretty sensible. But is it so clear-cut? MMR has been at the centre of an ongoing controversy since 1998, beset by claims that it causes autism and bowel disease in children who receive it. These theories, advanced primarily by gastroenterologist Dr Andrew Wakefield, have been vigorously rejected by the government, but many parents are unconvinced and confused. Take-up of the vaccine has fallen to 80% in some areas, precisely the sort of situation that can lead to outbreaks.
So is there any truth in Wakefield's claims? Like all other medications, the MMR vaccine went through clinical testing designed to spot adverse side-effects. Bowel disease and autism were not identified in any of the trials. The government alleged that this discredited the claims, and accused Wakefield of 'scaremongering'. A recent investigation by Channel 4 TV in the UK found that Wakefield had filed patents for a novel vaccine before publishing his claims.
There has been a great deal of confusion about the claims being made, with many commentators apparently under the impression that 'MMR causes autism'. The gist of the claim is that, very rarely, the MMR vaccine can produce an unusual form of inflammatory bowel disease. Symptoms include diarrhoea and bowel pain. The secondary claim is that this disease produces autism-like behaviour.
It is very difficult to assess the truth of the claims on the present evidence. In all the media furore, however, one key point has been neglected. The clinical trials of MMR monitored children for only 3 or 4 weeks after they received the vaccine. Bowel disease and autism emerge slowly and could have been missed.
Evidence from researchers around the world has been accumulated to support the MMR - inflammatory bowel disease link. An increasing number of children have the unusual bowel disease described, and it seems to be linked to the presence of measles virus in their intestine. Dr Timothy Buie, a paediatric gastroenterologist at Harvard, found chronic inflammation in the intestines of certain autistic children. However, large-scale epidemiological studies have repeatedly exonerated MMR of having any effect at the population level. The American Institute of Medicine examined 60 papers on the subject of MMR and bowel disease, and concluded '... the evidence is inadequate to accept or reject a causal relationship.'
So should students all heed the government's clarion call and obtain the MMR vaccine? Well, yes. Even if the scaremongers are correct and the MMR vaccine has a risk associated with it, it is accepted (even by Dr Wakefield and his allies) that this risk would apply only to a very small percentage of the population. Given the rapidity with which measles has erupted back onto the scene, it seems thoroughly sensible to accept the possible, tiny risk of the vaccine backfiring rather than the definite, sizeable risk of a measles epidemic.
In the longer term, there needs to be further government-funded research into the possibility of a link between MMR and inflammatory bowel disease. This proposal was supported by the American Institute of Medicine. Up to this point the government has been extremely bullish in its resistance, in an attempt to maintain public confidence in the vaccine. This strategy has backfired badly, possibly due to public mistrust following similar denials regarding BSE. Only with a thorough research programme will this controversy be laid to rest.
Statements and opinions expressed in this article are solely those of the author and may or may not be shared by David Bradley