Thimerosal
exposure from vaccines
Ts Bùi Quốc Quang
Thimerosal (sodium ethylmercury thiosalicylate) is an antimicrobial preservative
used since the 1930’s in numerous vaccines and medical preparations. Thimerosal
contains 49.6% mercury by weight and rapidly dissociates in aqueous solution
to ethylmercury and thiosalicylic acid.
Recently, concern has been raised about the possible contribution of ethylmercury
via childhood vaccinations with thimerosal-preserved vaccines to the etiology
of neurodevelopmental disorders, including autism. Although no direct
evidence has linked low levels of exposure to ethylmercury to autism,
thimerosal has been removed from childhood vaccines in the United States
due to public concern. However, removal of thimerosal from vaccines could
result in increased risk of microbial contamination or exposure to unknown
toxicants. At the present time, identifying an alternative to thimerosal
is still challenging. Consequently, thimerosal-preserved influenza vaccines
continue to be widely used.
In recent toxicology studies, administration of thimerosal to newborn
animals following modeled childhood vaccination schedules at 10 times
the levels of thimerosal found in childhood vaccines did not affect somatic
growth or the development of the central nervous system (Berman et al.,
2008). Further, no deficits were observed in tests of complex behaviors.
Although it’s true that ethylmercury is a neurotoxicant after repeated
exposure to high levels, the data in neonatal animals do not provide support
for the inference that neonatal exposure to thimerosal (e.g., low levels
of ethylmercury) is involved in the etiology of neurodevelopmental disorders.
Childhood vaccination is strongly recommended since the benefits outweigh
the risks and the concern of neurotoxicity from exposure to low levels
of ethylmercury in thimerosal is not substantiated.
Until the next time, stay healthy.
Ts Bùi Quốc Quang
Palo Alto, Feb 2008
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