(HealthDay News) — Compared with the general population, children with autism spectrum disorder (ASD) and their younger siblings are undervaccinated, according to a study published online March 26 in JAMA Pediatrics.

Ousseny Zerbo, Ph.D., from the Kaiser Permanente Vaccine Study Center in Oakland, Calif., and colleagues compared vaccination rates for children with ASD and their younger siblings with the general population in a retrospective matched cohort study.

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Data were included for 3,729 children with ASD, 592,907 children without ASD, and the younger siblings for both groups. The researchers found that children with ASD were significantly less likely to be fully vaccinated than children without ASD for vaccines recommended between ages 4 and 6 (adjusted rate ratio, 0.87). Vaccination rates were significantly lower among younger siblings of children with ASD versus younger siblings of those without ASD within each age category. The adjusted rate ratios varied from 0.86 to 0.96 for siblings younger than 1 year and for those aged 11 to 12 years, respectively. The likelihood of refusing at least one recommended vaccine for a younger sibling and likelihood of limiting the number of vaccines administered during the younger sibling’s first year of life were increased for parents of a child with ASD.

“The results of this study suggest that children with ASD and their younger siblings are at increased risk of vaccine-preventable diseases,” the authors write.

Several authors disclosed financial ties to the pharmaceutical industry.

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