Autism in the absence of MMR vaccine
Clinical bottom line
Autism rates in Japan continued to rise after the withdrawal of MMR vaccine.
H Honda et al. No effect of MMR withdrawal on the incidence of autism: a total population study. Journal of Child Psychology and Psychiatry 2005 doi: 10.1111/j.1469-7610.2005.01425.x
A link has been postulated between the specific use of the triple MMR vaccine and the rise of childhood autism. Though very considerable research has shown there to be no connection, some people continue to believe in such a link and they propose use of single vaccines instead. In Japan, MMR vaccine was introduced in 1989, but the programme was terminated in 1993 and only single vaccines used thereafter.
The experience of Japan therefore constitutes a real-world experiment of replacing triple MMR vaccine with single vaccines because of problems with production. If the proponents of a link between MMR and autism are correct, the result should be that cases of autism fall after withdrawal of MMR.
The study was conducted in a part of Yokohama with a population of about 300,000, and which was stable, or reflected changes typical for Japanese society as a whole, over the period of the study. The population was served by a special centre (Yokohama Rehabilitation Centre) that included a developmental psychiatry unit with early intervention services for developmental disorders. There was in place an early detection and intervention system that included specific routine checkups at four, 18 and 36 months, working to defined diagnostic criteria. At 18 months, about 90% of children participated in the programme, but those who did not, or those who were missed by the programme, could be referred by nurseries, paediatric clinics, or other services. These services began in 1987, two years before introduction of MMR.
Not only did the study have specific diagnostic criteria, therefore, but also ensured a complete coverage of a defined population, consistently over a period covering the introduction and withdrawal of the triple MMR vaccine.
Each birth cohort from 1988 to 1996 was followed up to age seven years, and results presented for all autistic spectrum disorders, for autism, and for autism associated with regression. The cumulative incidence per 10,000 children for each diagnosis was calculated for each year.
Over the whole period, and with full follow up to age seven years in birth cohorts from 1988 to 1996, 278 children developed autistic spectrum disorder, 158 autism, and 120 other autistic spectrum conditions. Of those with autism, 60 had definite regression and another 12 probable regression according to defined tests.
In the 1988 birth cohort, 70% of children had the MMR triple vaccine, falling to 1.8% in the 1992 birth cohort. Thereafter no children had the MMR triple vaccine (Figure 1).
Figure 1: Autistic conditions in birth cohorts to age seven years, and MMR vaccination rate in Japan: autism, all autistic spectrum disorders (ASD), and autism with regression
The incidence of all autistic spectrum disorders, and of autism, continued to rise after MMR vaccine was discontinued. The incidence of autism was higher in children born after 1992 who were not vaccinated with MMR than in children born before 1992 who were vaccinated. The incidence of autism associated with regression was the same during the use of MMR and after it was discontinued.
The increase of autistic spectrum disorders was evident in children with higher IQ.
The increase in autism and autistic spectrum disorders in this part of Yokohama displays the same increase over time seen in other parts of the world. Here, though, the increase occurred even when the MMR vaccine was withdrawn. This destroys any possible causative link between use of the vaccine and autism.
Perhaps the most important features of the study were that it comprehensively covered a population, and that the population was served by a special service testing children for developmental; disorders and using standard methods over the whole period. The quality and validity of the study is superlative, and the size good.
Whatever causes autism, it is not the MMR vaccine.