Background. Vaccine refusal is a global trend and was announced as one of the top ten health threats in recent years. The rate of vaccine refusal (VR) among children with autism spectrum disorders (ASD) has also increased in parallel with the global trend but their vaccination behavior may differ from that of the normal population. This study aims to determine the VR rates among parents of children with ASD, to define the risk factors for developing VR, and to evaluate the parental concerns for childhood vaccinations in this susceptible population.

Methods. We conducted a 4-part survey questionnaire among parents of children with ASD, evaluating the vaccination status for both the child with ASD and their younger sibling. The vaccination uptake of the first child was accepted as the `baseline` behavior, while the following sibling`s uptake was suggested as the `current` behavior. The risk factors of VR were determined with logistic regression analysis.

Results. The study group included 110 parents of children with ASD (M/F:76/34) and their younger siblings (M/F:57/53). The rate of `baseline VR` was 12.7 % whereas the `current VR` was 40% (p=0.001). High socioeconomic status (relative risk [RR]: 4.4; 95% confidence interval [CI]: 1.01-16.6; p=0.04), using social media as the main source of information (RR: 7; 95% CI: 1.5-32; p= 0.01) and lack of regular well-child visits of the sibling (RR: 25; 95% CI 4.1-166; p=0.001) were determined as risk factors for VR.

Conclusions. The vaccination behavior of parents changed after having a child with ASD, and thus, the younger siblings may constitute a risk group for VR. In clinical practice, pediatricians should be aware of this risk and evaluate the vaccination uptake of the younger siblings of children with ASD more carefully. Regular well-child visits and improving media literacy may be the key points to prevent VR in this susceptible population.

Keywords: autism spectrum disorder, childhood, vaccination behavior, vaccine refusal