November 14, 2002
Recently, there has been some confusion surrounding a
hypothesis that the vaccine preservative thimerosal is linked to
an increase in autism among children.
Neal Halsey,
MD, professor of
international health and director of the
Institute for Vaccine Safety at the Johns Hopkins
Bloomberg School of Public Health, does not and has
not supported the belief that thimerosal or vaccines themselves
cause autism in children, saying scientific evidence does not
suggest any causal association between any vaccine and autism.
Data published in the November 7, 2002, issue of the
New England Journal of Medicine conclusively showed
there was no difference in the rate of autism or related
disorders in children who received measles, mumps, and rubella
(MMR) vaccines compared to those who did not. Studies from other
countries have determined that the hypothetical association
between vaccines and autism was not supported by the available
evidence.
An article published in the November 10, 2002, issue of
New York Times Magazine included some statements
attributed to Dr. Halsey that misrepresented his opinion,
especially in the title and photo caption. A letter to the
editor has been submitted, to correct the misunderstandings that
have developed from this article.
Dr. Halsey does not believe that any vaccine increases the
risk of autism and he did not say that thimerosal, which
contains small amounts of ethyl mercury, represents a threat.
Thimerosal is not a threat because it is no longer used as a
preservative in vaccines administered to infants in the first 6
months of life, when there is increased susceptibility of the
developing brain to the effects of mercury and related
compounds.
In 1999, Dr. Halsey became concerned that the use of
thimerosal as a preservative in many vaccines led to some
children being exposed to more ethyl mercury than was
recommended based on guidelines from the
Environmental
Protection Agency for exposure to methyl mercury, a related
product. Recent studies have determined that children whoas
fetuses were exposed to low to moderate amounts of methyl
mercury through fish consumed by their mothers were at an
increased risk for having mild neurological learning
deficiencies. The findings from these studies did not show an
association between methyl mercury exposure and autism. The
Centers for Disease
Control and Prevention and the
National Institutes
of Health are supporting studies to determine if there is
any definitive evidence of mild neurodevelopmental delay
associated with the use of thimerosal as a preservative in
vaccines. The preliminary results from one of two unpublished
screening studies suggested the possibility of mild neurologic
impairment associated with exposure to multiple doses of
vaccines that contained thimerosal as a preservative, but there
was no suggestion of an increased risk of autism. These studies
require careful clinical evaluation of the exposed children
before any definitive conclusions can be made.
As a precaution and in an effort to make vaccines as safe as
possible, Dr. Halsey worked with the
American Academy
of Pediatrics and the Public Health Service in 1999 to urge
reductions in exposure to mercury in all forms for infants and
children and to discontinue using thimerosal as a preservative
whenever possible. Now all vaccines routinely administered to
infants and young children in the United States do not contain
thimerosal as a preservative.
More information can be found on the
Institute
for Vaccine Safety website or from a review of this issue
conducted by the
Immunization Safety Review Committee of the
Institute of
Medicine.
New York Times Correction 11/15/2002
Public Affairs Media Contacts for the Johns
Hopkins Bloomberg School of Public Health:Tim Parsons
or Kenna Brigham @ 410-955-6878 or
paffairs@jhsph.edu.
