Regressive autism is the rapid-onset loss of previously acquired milestones in central nervous system development often associated with seizures that occurs within the first 1-3 years of life. The dramatic CNS changes associated with regressive autism sometimes rapidly follow the administration of vaccines, highly suggestive of a causal connection that has been the subject of clinical studies worldwide; however, clinical research studies to date have failed to validate an association between vaccines and autism. Despite this, recent genetic studies have demonstrated extensive overlap of immune system components shown to be dysregulated in autism and those essential to the establishment of vaccine based immunity. Moreover, the genetic links between autism and the immune system extend to physiological differences in immune system functions that may directly affect central nervous system maturation during critical developmental windows. In this model, vaccine-associated regressive autism (VARA) is the result of the combined effects of predisposing genetic (and/or other) epidemiological factors on immune system functions that predispose at-risk individuals to central nervous system impairment following the administration of routine childhood vaccines.