Review of scientific data may allay parental concerns on vaccine
safety After reviewing dozens of scientific studies, a leading vaccine expert concludes that preservatives, additives and other substances contained in vaccines pose very little risk to children receiving those vaccines.
In addition to the primary ingredient that stimulates a protective
immune response, various vaccines may contain small amounts of metals, proteins, and other chemicals, some of which are residual by-products of
normal vaccine manufacturing. “Parents can be reassured that the trace
quantities of mercury, aluminum and formaldehyde contained in vaccines
will not harm their children,” says the study’s lead author, Paul A. Offit,
M.D., chief of Infectious Diseases and director of the Vaccine Education
Center at The Children’s Hospital of Philadelphia.
The article, which summarizes studies of human and animal exposures, appears in the December 2003 issue of Pediatrics. Dr. Offit’s co-author is pharmacist Rita K. Jew, Pharm.D., also of The Children’s Hospital of Philadelphia.
Of the substances studied, say the authors, only gelatin proteins
and egg proteins are known to have harmful effects while in vaccines, but
such effects are very rare. Those proteins may cause severe hypersensitivity
reactions in children with allergies to gelatin or eggs. Dr. Offit adds
that physicians should take appropriate safeguards for children known to have
those allergies. For instance, children with allergies to the egg
protein found in influenza vaccine can be desensitized to the vaccine.
One controversial vaccine-related substance is thimerosal, a
compound of mercury used as a preservative to prevent contamination by bacteria or fungi. It has received considerable scrutiny by Congress and the news
media since its removal from most U.S. childhood vaccines in 2001. Thimerosal
was removed from vaccines as a precaution, even though there has never been
scientific evidence of a link between thimerosal and adverse effects.
One confusing element, say the authors, is an incorrect assumption
that ethylmercury, contained in thimerosal, has the same effects as
methylmercury, a more toxic mercury compound found in the environment,
but not in vaccines. “An important difference is that the body eliminates
ethylmercury far more quickly than it eliminates methylmercury,” adds
Dr. Offit.
Other substances found in vaccines, in addition to the active
agent designed to stimulate a protective response, are additives, adjuvants
and manufacturing residuals.
Additives, which include various sugars, amino acids and proteins,
are used to stabilize vaccines during processing and storage. Except for
very rare hypersensitivity reactions to gelatin proteins, vaccine additives
have not been associated with disease.
Adjuvants, such as aluminum compounds, enhance the desired immune
response the vaccine is designed to produce. “The safety of aluminum has
been established by experience over the past 70 years with hundreds of
millions of people inoculated with aluminum-containing vaccines,” say
the authors, who add that the small quantities of aluminum in vaccines have
not been shown to be harmful in animal studies.
Substances remaining in vaccines as residuals of the manufacturing
process may include antibiotics, formaldehyde, and egg and yeast
proteins.
With the exception of the very rare reactions caused by egg proteins,
the quantities of other residual substances are too small to demonstrate any
documented reactions in those receiving the vaccines.
“Based on the best available scientific evidence,” concludes Dr.
Offit, “parents can be confident that vaccines are overwhelmingly safe,
as well as effective in preventing infectious diseases.”