Immunization Uptake in Siblings of Children with Autism

Background: Fears persist that vaccinations increase risk of autism spectrum disorders (ASD), despite epidemiological evidence to the contrary. Immunization rates have declined in many countries although data do not suggest risk. No one experiences these concerns more deeply than parents of children with ASD as they face the decision about whether to vaccinate younger siblings.
Objectives: To compare the immunization uptake of younger siblings of children with ASD to those of affected siblings and low-risk controls.
Methods: Participants included 160 younger siblings of children diagnosed with ASD (‘high-risk siblings’), 91 of the affected older siblings (‘probands’), and 56 low risk controls (‘controls’; no family history of ASD). Data on immunization status were obtained from medical records; specifically, the receipt/non-receipt and timing of administration of the Diphtheria, Pertussis, Tenanus and Polio (DPTP) and Measles, Mumps and Rubella (MMR) vaccines. Immunization was classified as ‘incomplete’ if a vaccine was not received, and as ‘delayed’ if a vaccine was received at least 3 months late relative to current Canadian guidelines (2, 4, 6, 18 months for DPTP; 12 months for MMR). Each participant was at least 18 months old at the time of data collection. Results: Of the high-risk siblings, 86 of 160 (53.8%) had records indicating delayed or incomplete immunization on either vaccine, in comparison to 20 of 91 probands with ASD (22%), and 5 of 56 low-risk controls (8.9%). Similar coverage rates were identified for DPTP and MMR vaccines in high-risk sibs (delayed or incomplete, respectively).

Conclusions: It appears that concerns regarding vaccinations and risk of ASD persist among families of children with ASD, as younger siblings have decreased and delayed uptake of vaccinations compared to older siblings and low-risk controls.