Children with autism spectrum disorder (ASD) and their younger siblings were undervaccinated compared with the general population, a recent study found. Researchers conducted a retrospective matched cohort study within 6 integrated health care delivery systems across the US within the Vaccine Safety Datalink. Participants were children born between January 1, 1995, and September 30, 2010, and their younger siblings born between January 1, 1997, and September 30, 2014. Included were 3,729 children with ASD (676 [18.1%] female), 592,907 children without ASD, and their respective younger siblings. They found:

• For vaccines recommended between ages 4 and 6 years, children with ASD were significantly less likely to be fully vaccinated compared with children without ASD.
• Within each age category, vaccination rates were significantly lower among younger siblings of children with ASD compared with younger siblings of children without ASD.
• Parents who had a child with ASD were more likely to refuse at least 1 recommended vaccine for that child’s younger sibling and to limit the number of vaccines administered during the younger sibling’s first year of life.