To the Editor: Dr Hviid and colleagues1 found no increase in relative risk of core autism
from thimerosal in vaccines using the Danish autism registry. Denmark removed
thimerosal from infant vaccines in mid-1992. The findings of Hviid et al are
based on finding fewer older (born 1990-1992) thimerosal-exposed children
than younger (born 1992-1996) unexposed children in the 2000 registry year.
However, a sizable percentage of autism cases, skewing toward older children,
are lost from the registry each year. Thus, the authors' finding is likely
to be biased due to incomplete recordkeeping.
Bernard S. Association Between Thimerosal-Containing Vaccine and Autism. JAMA. 2004;291(2):180. doi:10.1001/jama.291.2.180-b