Objectives: The primary goal of this study is to examine the relationship between the frequency and number of childhood immunizations and the subsequent likelihood of developing autism. In addition, this study aims to investigate the relationship between childhood vaccines and disorder severity in children who do go on to develop autism.
Methods: Immunization data were collected for 91 children divided among the following three groups: (1) siblings of children with an autism spectrum disorder diagnosis, (N =48; gender = 37M); (2) children at risk for developmental delays (N = 7; gender = 5M); and (3) children expected to develop typically (N = 36; gender = 19M). All children were at least 2 years of age when their immunization records were collected. Individual immunization data were recorded and then compared with diagnostic outcome and behavioral data.
Results: Tests of association and linear multiple regressions revealed that neither a greater number of childhood vaccines nor a higher rate of vaccination had a positive relationship with subsequent autism spectrum diagnosis (N=8; gender=7M) or disorder severity, which was assessed in all participants. In addition, comparison of immunization data to behavioral indicators at 2 years of age did not reveal any relationship between either higher frequency or greater number of childhood vaccines and subsequent negative behavioral outcomes. Likewise, neither vaccination with MMR nor the age of MMR vaccination was significantly related to outcome. Instead, because siblings of children with autism were less likely to be vaccinated according to the recommended schedule, both correlations and multiple regressions revealed a significant relationship between higher rates of vaccination and non-ASD behavioral outcomes.
Conclusions: These results suggest that childhood vaccines do not increase children’s risk of developing autism and do not exacerbate the disorder severity in children who are later diagnosed with autism. Children who receive a greater number of vaccines overall, who receive the MMR vaccine, or who receive immunizations at a higher rate, do not differ significantly on subsequent behavioral measures from children who receive vaccines on an alternative schedule or children who do not receive vaccines. Instead, the results of this study emphasize heritability in risk for autism, and also indicate that siblings of children with an autism diagnosis are less likely to be vaccinated, which actually increases their risk for contracting other illnesses.
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