according to findings published March 26 in JAMA Pediatrics.
In a matched cohort study of 3,729 children with autism spectrum disorder (ASD) and 592,907 children without ASD, children with ASD were significantly less likely than children without ASD to be fully vaccinated for vaccines recommended at 4-6 years of age (adjusted rate ratio = 0.87; 95% confidence interval 0.85-0.88; P less than .05), wrote Ousseny Zerbo, PhD, of the Kaiser Permanente Vaccine Study Center in Oakland, Calif., and his coauthors.
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ASD was defined based on ICD-9-CM codes 299.0, 299.8, and 299.9 in EHRs at least twice from birth until either the patient’s 6th birthday or follow-up, whichever came first. Assessment included the Centers for Disease Control and Prevention’s ACIP (Advisory Committee Immunization Practices)–recommended vaccinations for ages 4-6 years and 11-12 years. Children who received all doses within the ACIP-recommended age limits were considered fully vaccinated, the investigators said.
Only 81.6% of children with ASD had received all recommended doses between ages 4 and 6 years, compared with 94.1% of children without ASD. For the MMR vaccine, 84.0% of children with ASD aged 4-6 years were vaccinated, compared with 95.9% of children without ASD. For vaccines recommended at 11-12 years of age, the proportion of children with and without ASD receiving all vaccines were 77.5% and 76.9%, respectively, and adjusted RR was not significant, Dr. Zerbo and colleagues reported.
In all age groups, the proportion of fully vaccinated children was lower among the younger siblings of children with ASD, compared with the younger siblings of children without ASD. The largest differences in vaccination rates were seen in children aged 1-11 months and 1-2 years, with 73.2% of ASD siblings and 85% of non-ASD siblings aged 1-11 months being fully vaccinated (aRR, 0.86; 95% confidence interval, 0.82-0.89), and 60.2% of ASD siblings and 70.7% of non-ASD siblings aged 1-2 years being fully vaccinated (aRR, 0.84; 95% CI, 0.79-0.89), the authors noted.
Although most parents vaccinate their children in accordance with the ACIP-recommended schedule, the results of this study suggest that for siblings of children with ASD, “the ASD diagnosis of the older sibling may have contributed to the undervaccination of the younger children,” Dr. Zerbo and his colleagues wrote.