Implications for practice and research >The younger siblings of children who received an autism spectrum diagnosis are shown to have lower vaccination rates than the younger siblings of children who have not received an autism spectrum diagnosis. The benefit of applying this knowledge in practice would be to take steps to target this subpopulation. >The research is novel in that previous studies were not as large or focused. The retrospective matched cohort study uses ‘Vaccine Safety Datalink’ information from six integrated healthcare delivery systems across the USA. >Future research could explore strategies for engaging with parents who have received an autism spectrum diagnosis for older children when considering vaccinating younger siblings. To read the full article, log in using your NHS OpenAthens details.