EVALUATING THE EVIDENCE
Smeeth and colleagues abstracted data from the General Practice Database of the United Kingdom between 1987 and 2001, searching for children with the diagnosis of a PDD.6 A total of 5,763 children in the United Kingdom were evaluated; 1,294 cases in which the child had a known diagnosis of a PDD and 4,469 case controls were included. The study found 1,010 (78.1%) cases in which the child
had the MMR vaccination prior to the recorded diagnosis, compared with 3,671 (82.1%) controls who had the MMR vaccination before the age at which their matched control was diagnosed. The odds ratio for the association between the MMR and a PDD was 0.86 (95% confidence interval [CI], 0.68-1.09). The findings were similar when restricted to children with a diagnosis of autism. This study found that the risk of developing autism was similar in vaccinated and unvaccinated children. The MMR vaccine was not associated with an increased risk of subsequent PDD
diagnosis. The study found no convincing evidence that MMR vaccination increases the risk of autism or other PDDs.
In another study, Fombonne and colleagues evaluated 27,749 children who were born in Canada between 1987 and 1998.7 This study identified 180 children with a PDD, resulting in a prevalence for PDD of 64.9 per 10,000 population. The prevalence of PDD in thimerosal-free birth cohorts was significantly higher than that in thimerosal-exposed cohorts: 82.7 of 10,000 (95% CI, 62.0-108.0) compared with 59.5 of 10,000 (95% CI, 49.6-70.8). During the 11-year study, rates of PDD significantly increased whereas MMR vaccinations showed a slight opposite trend. This makes the association between the MMR vaccine and autism less plausible. The researchers' findings ruled out an association between PDDs and the MMR vaccination.
Madsen and colleagues evaluated the largest number of patients in a retrospective cohort study from Denmark. This study surveyed 537,303 children, 82% of whom had received the MMR vaccine. Each case was evaluated for autism and PDDs.8 Of the 537,303 children in the cohort evaluated from January 1991 to December 1998, 440,644 had received the MMR vaccine. There were 316 children identified as having autism and 422 children identified as having autistic spectrum disorders. Compared with the unvaccinated group, the relative risk of autism in the group vaccinated with MMR was 0.92 (95% CI, 0.68-1.24), and the relative risk of a different autistic spectrum disorder was 0.83 (95% CI, 0.65-1.07). Overall, there was no increased risk of autism or autism-related disorders between vaccinated children and unvaccinated children. During the 7 years of the study, no temporal clustering of autism cases was observed at any time after immunization. This study found no causal relationship between the MMR vaccination and autism.
RETRACTION OF THE WAKEFIELD PAPER
In February 2010, The Lancet issued a retraction of the 1998 Wakefield study. The editors of The Lancet issued the following statement:
Following the judgment of the UK General Medical Council's [GMC's] Fitness to Practise Panel on Jan 28, 2010, it has become clear that several elements of the 1998 paper by Wakefield et al are incorrect, contrary to the findings of an earlier investigation. In particular, the claims in the original paper that children were "consecutively referred" and that investigations were "approved" by the local ethics committee have been proven to be false. Therefore we fully retract this paper from the published record.9
In 2004, 10 of Wakefield's 13 coauthors disavowed the findings of the 1998 study. In 2009, the US "vaccine court" rejected US lawsuits claiming that there was a plausible link between the vaccine and autism.10 The GMC's final conclusion was that Wakefield misled The Lancet about how children came to be studied, that the ethical statement in the paper was false, and that the hospital where the research was conducted had not approved it. The GMC found that Wakefield "showed a callous disregard for the distress and pain that he knew or ought to have known the children involved might suffer, that he abused his position of trust as a medical practitioner, and that he brought the medical profession into disrepute."11
CLINICAL BOTTOM LINE
The evidence clearly shows that there is no link between vaccination against measles, mumps, and rubella, and an increased risk for the development of a PDD, such as autism. JAAPA
REFERENCES
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3. Centers for Disease Control and Prevention (CDC). Prevalence of autism spectrum disorders—autism and developmental disabilities monitoring network, United States, 2006. http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5810a1.htm. Last reviewed December 10, 2009. Accessed May 11, 2010.
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8. Madsen KM, Hviid A, Vestergaard M, et al. A population-based study of measles, mumps, and rubella vaccination and autism. N Engl J Med. 2002;347(19):1477-1482.
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445. http://dx.doi.org/10.1016/S0140-6736(10)60175-4.
10. U.S. Court of Federal Claims. Autism decisions and background information. http://www.uscfc.uscourts.gov/sites/default/files/vaccine_files/Background_on_the_autism_
proceedings.pdf. 2009. Accessed May 11, 2010.
11. General Medical Council. Fitness to Practise Panel in the case of Dr Andrew Jeremy Wakefield. http://www.gmc-uk.org/concerns/hearings_and_decisions/data/5614.asp.
January 28, 2010. Accessed May 11, 2010.