The mercury-containing vaccine preservative thimerosal has also been suggested to be linked to autism. This is based on an FDA report from 1999 suggesting that the concentrations of ethylmercury, a thimerosal metabolite, exceeded acceptable levels as determined by the Environmental Protection Agency (EPA). However, the EPA recommendations are based on data for methylmercury, a common environmental toxin. In contrast, thimerosal is metabolized to ethylmercury, which is excreted much more quickly and has not been associated with neurodevelopmental delay. Nevertheless, because of the theoretical concern of thimerosal in childhood vaccines, it has been removed from all childhood vaccines, except some influenza vaccines, for more than a decade. This has not had an impact on rates of autism. Since then, multiple large epidemiologic studies have confirmed that thimerosal exposure is not associated with autism. Despite these reassuring data, some parents still have concerns about thimerosal in influenza vaccines. For these parents, LAIV, which is recommended for children as noted previously, or single-use vials that do not contain thimerosal may be used.