Thimerosal is an ethylmercury (49.55%
mercury by weight) preservative historically added to some
vaccines. Toxicokinetic studies showed children in the United States received doses of
mercury from
Thimerosal-containing
vaccines (
TCVs) in excess of safety guidelines. In the United States during the 1990s,
diphtheria-
tetanus-
pertussis (DTP) and Haemophilus influenzae type b (Hib)
vaccines (maximally, 50 mug
mercury per joint administration) and
diphtheria-
tetanus-
pertussis-Haemophilus influenzae type b (DTPH)
vaccines (25 mug
mercury per administration) were given to children in the same childhood vaccination schedule at 2, 4, 6, and 15-18 mo, so that children receiving DTP and Hib
vaccines may have maximally received an additional 100 mug more
mercury exposure from
TCVs than children administered DTPH
vaccines. A case-control epidemiological study of
neurodevelopmental disorders (
NDs) reported to the
Vaccine Adverse Event Reporting System (VAERS) (online public access version; updated 31 August 2004) following administration of DTP
vaccines in comparison DTPH
vaccines manufactured by Lederle Laboratories (Pearl River, NY) from 1994 through 1998 was undertaken. Significantly increased odds ratios for
autism,
speech disorders,
mental retardation,
infantile spasms, and thinking abnormalities reported to VAERS were found following DTP
vaccines in comparison to DTPH
vaccines with minimal bias or systematic error. Additional ND research should be undertaken in the context of evaluating
mercury-associated exposures, especially since in 2005 the Institute of Medicine issued a report calling into question handling of
vaccine safety data by the National Immunization Program of the Centers for Disease Control and Prevention.