Pediatric vaccines have been considered controversial due to potential negative effects on development, particularly impaired social interaction and communication, hyperactivity, and repetitive stereotyped behaviors that are characteristic of autism spectrum disorder (ASD). Some reports suggest that exposure to ethyl mercury (EtHg), in the form of thimerosal, in pediatric vaccines may play a causative role in such negative effects. Male infant rhesus macaques (n = 79) were assigned at birth to one of six study groups (12–16 subjects/group) as follows: (1) the pediatric vaccination schedule from the 1990s including thimerosal-containing vaccines (TCVs), (2) the same 1990s schedule but accelerated to accommodate the developmental trajectory of the infant rhesus macaque, (3) TCVs only (saline placebo for Mumps–Measles–Rubella [MMR]), (4) MMR only (other injections replaced with saline placebo), (5) the expanded vaccine regimen from 2008 (where fewer vaccines contained thimerosal), or (6) a control group following the 1990s schedule with all vaccines replaced with saline placebo. Subjects began socializing at approximately 25 days of age and were socialized 5 days per week in a 4-monkey peer group. Social behavior data, collected between 15 and 18 months of age using a computer system capturing a variety of social and non-social behaviors, were included in this analysis. Data were analyzed using repeated measure ANOVAs with Dunnett’s test post-hoc procedures following significant experimental group or group × age interactions. No significant differences in non-social or social behavior were found when comparing the animals in the vaccine groups to controls. The data do not provide any evidence of abnormal social behavior in rhesus macaques exposed to low-dose thimerosal and should provide reassurance that TCVs do not contribute to the negative effects associated with ASD. Support from the Johnson Family, the Ted Lindsay Foundation, and SafeMinds is gratefully acknowledged.
Copyright © 2014 Published by Elsevier Inc.