AUTISM

Epidemiologic Evidence

The committee reviewed 22 studies to evaluate the risk of autism after the administration of MMR vaccine. Twelve studies (Chen et al., 2004; Dales et al., 2001; Fombonne and Chakrabarti, 2001; Fombonne et al., 2006; Geier and Geier, 2004; Honda et al., 2005; Kaye et al., 2001; Makela et al., 2002; Mrozek-Budzyn and Kieltyka, 2008; Steffenburg et al., 2003; Takahashi et al., 2001, 2003) were not considered in the weight of epidemiologic evidence because they provided data from a passive surveillance system lacking an unvaccinated comparison population or an ecological comparison study lacking individual-level data. Five controlled studies (DeStefano et al., 2004; Richler et al., 2006; Schultz et al., 2008; Taylor et al., 2002; Uchiyama et al., 2007) had very serious methodological limitations that precluded their inclusion in this assessment. Taylor et al. (2002) inadequately described the data analysis used to compare autism compounded by serious bowel problems or regression (cases) with autism free of such problems (controls). DeStefano et al. (2004) and Uchiyama et al. (2007) did not provide sufficient data on whether autism onset or diagnosis preceded or followed MMR vaccination. The study by Richler et al. (2006) had the potential for recall bias since the age at autism onset was determined using parental interviews, and their data analysis appeared to ignore pair-matching of cases and controls, which could have biased their findings toward the null. Schultz et al. (2008) conducted an Internet-based case-control study and excluded many participants due to missing survey data, which increased the potential for selection and information bias.

The five remaining controlled studies (Farrington et al., 2001; Madsen et al., 2002; Mrozek-Budzyn et al., 2010; Smeeth et al., 2004; Taylor et al., 1999) contributed to the weight of epidemiologic evidence and are described below.

Taylor et al. (1999) conducted a self-controlled case-series study in children with autistic disorders residing in the North East Thames region of the United Kingdom. The children were identified from computerized special needs or disability registers. A total of 498 children who were born from 1979 through 1998 and had an autism diagnosis before 16 years of age were included in the analysis. After reviewing the clinical records, the investigators confirmed that the autism diagnoses met the criteria of the International Classification of Diseases, 10th revision (ICD-10) in 82 percent of typical autism cases and 31 percent of atypical autism cases (the authors used the term core to describe typical autism, as noted in the methods). The self-controlled analysis investigated the risk of typical or atypical autism diagnosis among 357 cases during two postvaccination periods (12 or 24



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