Debunking the MMR-Autism myth



Measles vaccine ranks as one of the safest and most effective of vaccines. In large parts of the developed world the virus has been eliminated or is close to be eliminated by concerted and intensive vaccination campaigns. In South Africa much has been achieved in controlling measles by routine as well as mass immunization programmes, to the extent that the disease is now rarely seen in this country. The virus is however one of the most contagious of all viruses and very high immunization rates are required to reach a level of herd immunity to ensure control and eventually elimination and even eradication of infection. To achieve this parents and caregivers need to have trust in the safety of the vaccine and confidence in its efficacy.

In 1998, Dr Andrew Wakefield of the Royal Free Hospital in London gave a press conference in which he cast doubts on the safety of MMR vaccine. The effect of this on the British public was dramatic and significantly threatened to undo much of the extraordinary achievements in the worldwide control of measles. Remarkably, Wakefield's claim was based on observations of only twelve children and it purported to demonstrate that there was an association between MMR vaccine and autism and chronic intestinal abnormalities (A similar concern had been expressed at an earlier stage because of the awareness of encephalitis as a rare complication of measles disease). This association was quickly disproved by an epidemiological study carried out by different research groups of the same institution. Subsequently a number of studies in various parts of the world have provided strong epidemiological evidence against any causal association between MMR and either autism or chronic bowel disease. One of the most extensive of these studies has provided particularly strong evidence against the MMR-autism link. This retrospective cohort study carried out in Denmark involved 537,303 children, 82% of whom had received the MMR vaccine. The relative risk of autistic disorder in vaccinated children, compared to the unvaccinated children was 0.92. In other words if anything, the risk of developing autism was marginally lower in children who had been vaccinated.

However, despite very strong epidemiological evidence, disproving a causal association as well as biological implausibility, the myth of MMR causing autism has persisted, predominantly in the United Kingdom. The hypothesis is that in selected children with immunological aberrations the antigenic overload of administering a combination of three foreign antigens may trigger an auto-immune response in the brain precipitating a novel form of autism, which is also associated with chronic bowel abnormalities. As a result two groups of MMR vaccine objections were born - those who still wish their children to receive each of the three components of MMR but as separate vaccines, and a second group who refuse all vaccines. Single vaccines are difficult to obtain in the United Kingdom and many children have as a result missed out on vaccination altogether. Following on this there has been an alarming increase in notified measles and mumps and several outbreaks have been reported in the United Kingdom.

To compound the difficulty, the incidence of autism has apparently increased over recent years due to improvements in reporting and a wider use in the diagnosis of autism to embrace children with unexplained cognitive and behavioural disorders.

Unfortunately, MMR-autism has now joined the ranks of the other myths and misconceptions, which are repeatedly propounded by the increasingly vocal anti-vaccination groups, such as DPT causing SIDS. Many of these alleged adverse effects arise from the logical fallacy of post-ergo propter hoc i.e. "after this, therefore because of this", which mistakes association for causation. Routine immunization programmes administer vaccines on at least twelve occasions in the first two years of life - precisely the same time as many childhood events occur. The chances of a fortuitous association between receiving a vaccine and developing afflictions such as autism are therefore not remote.

In an age of powerful television messages and an internet which has over thirty dedicated anti-vaccination sites and some 300 more advocating an anti-vaccination message, healthcare workers have a important responsibility to build trust in parents and caregivers. "New Age" thinking delivers strong messages promoting "informed choice" in advising parents to "play it safe" and avoid vaccinating their children. "Free-loading" has also become popular as the visible affects of the diseases have all but disappeared and "as long as everyone else gets the vaccine there is no reason my child should get it". This, it must be pointed out, is a serious mistake. Even in countries with high vaccination coverage, such as the USA, it has been shown that measles is 35-times more common in those choosing exemption from compulsory vaccination, as compared to vaccinated children.

Visual images and vivid accounts of families living with children with autism are indeed distressing, anecdotes are not proof. On the other hand there could be no more heart-rending tragedy than a child damaged by a disease, which could so easily have been prevented by a simple vaccine.