New studies show no link between MMR and autism
Published:
The first study was carried out by Makela and colleagues in Finland and published in the journal Pediatrics. The authors examined the records of over 500,000 Finnish children who had received MMR and looked at whether or not these children were admitted to hospital for aseptic (i.e. viral) meningitis, encephalitis or autism. MMR is known to protect against encephalitis due to measles, mumps and rubella. The authors found that aseptic meningitis rates decreased by 35% and encephalitis rates by 25% after the introduction of MMR.
The authors did not find any association between hospitalisation for autism and time since vaccination with MMR. None of the 309 children identified in the study with autism were admitted to hospital at any time because of inflammatory bowel disease.
While these results add to the already large body of evidence showing no association between MMR and autism this study has some limitations, as identified by the authors. The main one is that they only looked at hospital admissions. Thus they might have missed children with autism who were not admitted to hospital. However they do point out the hospital admission is a common part of the initial management of autism in Finland.
The second study, published in the New England Journal of Medicine, is even more comprehensive. Madsen and colleagues studied all children born in Denmark between 1991 and 1998. The vaccination records of over 500,000 children were examined. They also looked at the admission records of psychiatric hospitals, psychiatric departments and outpatient departments to identify cases of autism and autism spectrum disorder (ASD). There are a number of factors specific to Denmark relevant to this study: autism can only be diagnosed by child psychiatrists, children with suspected autism are routinely referred to such specialists and there is a virtually complete reporting of childhood vaccination. These factors, combined with the fact that the authors were able to examine results for all children born in Denmark, make this a very robust study.
Madsen and colleagues found that the risk of autism was the same in vaccinated and unvaccinated children. They also found that there was no association between the age that MMR was given, time since vaccination or the date of vaccination and the development of autism. There was no evidence to suggest that there could be a subgroup of children who are particularly at risk of developing autism after MMR.
All of the studies published to date that have investigated possible links between MMR and autism have found no association. The study by Madsen and colleagues was very well-designed and extremely comprehensive and probably represents the best evidence yet that there is no association between MMR and autism.
