Objectives: This study compares the immunization practices of preschoolers with ASD and typical development (TD).
Methods: Immunization records were abstracted from 240 (161 ASD, 79 TD) children between the ages of 24.1-54.4 months participating in the Autism Phenome Project from April 2006 to August 2011. Seventy-eight percent were male. We compared immunization rates for the vaccines required by the State of California for children ages 18 months to 5 years (3 doses of Hep B, 4 DTAP, 4 Hib, 4 PCV, 3 IPV, and 1 MMR). Of note, there was a national HIB vaccine shortage from 2007-2009. Varicella was not included due to the possibility of naturally acquired immunity.
Results: Immunization rates in ASD children were slightly lower than in TD (see Table 1), but this difference was not statistically significant, with the exception of Hep B, where 91.3% of children with ASD had received 3 doses compared to 98.7% of TD (p=0.024). These rates were at or above those reported in the 2011 National Immunization Survey (NIS). One (0.6%) ASD child had not received any immunizations. The national rate for children who received no immunizations was 0.8%.
Conclusions: Despite the lack of evidence supporting any causal relation of vaccines to ASD (IOM, 2011) many parents remain concerned and some choose to delay or avoid vaccines. Immunization rates in preschoolers with ASD in our sample were generally lower than TD, although there were no statistically significant differences except for Hep B. Our study, although not designed to specifically address a causal relationship, does not support an association between vaccines and ASD. In most cases, these immunization practices represent behavior during the first 18 months of life prior to receiving an ASD diagnosis. Further study looking at differences in vaccine acceptance during the 4-6 year booster period is warranted, as having an ASD diagnosis may affect parents’ attitudes towards future immunization.
| ASD (n=161) | TD (n=79) | p-value | 2011 NIS | |
| Hep B | 147 (91.3%) | 78 (98.7%) | 0.024 | 91.1% |
| DTAP | 150 (93.2%) | 78 (98.7%) | 0.110 | 84.6% |
| Hib | 107 (66.5%) | 48 (60.8%) | 0.386 | shortage 2007-09 |
| PCV | 134 (83.2%) | 66 (83.5%) | 0.128 | 84.4% |
| IPV | 149 (92.5%) | 78 (98.7%) | 0.066 | 93.9% |
| MMR | 151 (93.8%) | 75 (94.9%) | 0.99 | 91.6% |
See more of: Epidemiology
See more of: Prevalence, Risk factors & Intervention