It is now ten years since a study, in the Lancet, triggered concern of a link between the MMR vaccine and the development of autistic spectrum disorder (ASD).¹ A subsequent virological study was cited as evidence that supported this association.² These studies were viewed with scepticism at the time because of the lack of clinical and technical validation and detail, and a recent review of the methods used discredited them.³

The Baird et al study⁴ was a case-control, community-based study in the UK. It included 240 children aged 10-12 years who had been vaccinated with at least one dose of MMR. Of these children, 98 had ASD, 52 had special educational needs but no ASD, and 90 were typically developing controls. The study found no difference in the distribution of the measles antibody or virus in children with ASD compared with controls. These findings were not affected by the number of MMR vaccinations the child had had.

There is now an overwhelming body of evidence that has found no link between MMR and autism. Studies examining time trend links between ASD and MMR have failed to find an association between the introduction⁵ or cessation⁶ of MMR vaccination and the rate of autism diagnosis, and a large case-control study in the UK reported no association between patient vaccination and ASD diagnosis.⁷ Biological studies, using methods designed specifically to identify the measles virus, have also failed to find evidence of its persistence in peripheral blood.^8,9 The SNAP study found no difference in the level of circulating measles virus, or of an altered immune response, between children with ASD and controls.¹⁰

The controversy over MMR vaccination has had significant consequences for MMR uptake in the UK. Following its introduction in 1988, the MMR programme had been effective in controlling measles; only a small number of cases, linked to importation, were recognised. A mass campaign in 1994 successfully vaccinated 92% of children targeted, and led to the interruption of measles transmission in the mid-1990s.

There has been a significant drop in vaccine coverage since 1998, particularly in parts of London.¹¹ The consequences are inevitable. A rise in measles cases has been seen over the past few years as susceptible patients have built up in the population.¹² Indigenous circulation of measles is now re-established, and the consequential burden of disease will follow unless improved coverage can be achieved. Several factors are likely to have contributed to the drop in vaccine uptake, including changes in services delivering the vaccines.

There is still general public concern about the risk of MMR vaccination, which is reflected in parental decisions,¹³ although there has been some return in parental confidence.¹⁴ In the Baird et al study, in which children received MMR1 prior to the study suggesting a link with autism, there was lower uptake of MMR2 among both children with ASD and children with special educational needs but no ASD. This may reflect parental concern about vaccination following a diagnosis of developmental abnormality, and GPs should address this directly with parents.

Parents most frequently refer to primary healthcare professionals, in particular health visitors and GPs, as their source of information about immunisation. Despite the strength of the evidence that does not support a link between the MMR vaccination and ASD, and extensive national debate, the failure to improve coverage significantly highlights the vital role of primary care in making evidence-based advice available to parents regarding MMR immunisation; specifically that there is no support for an association with ASD. The decision by parents not to vaccinate is often a conscious choice against immunisation¹⁵ and primary healthcare professionals should encourage a dialogue. The opportunity to make a real difference to public health exists.