pediatrics
Vaccine Hesitancy
Thimerosal and Autism
Thimerosal is a mercury compound previously used as a preservative in many multidose vaccine vials; preservatives are not needed in single-dose vials and cannot be used in live-virus vaccines. Thimerosal is metabolized to ethylmercury, which is eliminated quickly from the body. Because environmental methylmercury (which is a different compound that isnoteliminated from the body quickly) is toxic to humans, there was concern that the very small amounts of thimerosal used in vaccines might cause neurologic problems, particularly autism, in children. Because of these theoretical concerns, even though no studies had shown evidence of harm, thimerosal was removed from routine childhood vaccines in the United States, Europe, and several other countries by 2001. However, in these countries, small amounts of thimerosal continue to be used in certain influenza vaccines and in several other vaccines intended for use in adults. For information about vaccines that contain low levels of thimerosal in vaccines, see theFDA: Thimerosal and Vaccines. Thimerosal is also used in many vaccines used in resource-poor countries; the World Health Organization (WHO) has not recommended its removal because there is no clinical evidence of toxicity due to routine use. Despite the removal of thimerosal, rates of autism have continued to increase, strongly suggesting that thimerosal in vaccines does not cause autism. Also, 2 separate Vaccine Safety Datalink (VSD) studies have concluded that there is no association between thimerosal and autism. In a cohort study of 124,170 children in 3 managed care organizations (MCOs), Verstraeten et al found no association between thimerosal and autism or other developmental conditions, although inconsistent associations (ie, seen in one MCO but not another) were seen between thimerosal and certain language disorders ( Thimerosal and autism references ). In a case-control study of 1000 children (256 with an autism-spectrum disorder and 752 matched controls without autism), Price et al, using regression analysis, found no association between exposure to thimerosal and autism ( Health care professionals who work with parents who are still concerned about thimerosal in the influenza vaccine may use single-dose vials of injectable vaccine or the live-attenuated nasal spray vaccine, neither of which contains thimerosal. 1.Verstraeten T, Davis RL, DeStefano F, et al: Safety of thimerosal-containing vaccines: A two-phased study of computerized health maintenance organization databases.Pediatrics112:1039-1048, 2003.Clarification and additional information.Pediatrics113(1):184, 2004. 2.Price CS, Thompson WW, Goodson B, et al: Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism.Pediatrics126(4):656-664, 2010. doi: 10.1542/peds.2010-0309 