270 Vaccines and Autism
increases the chances of developing an antibiotic resistance and the introduc-
tion of genetically modified DNA and RNA is risky in the sense that it may
take years to fully understand the pros and cons of inserting foreign genes into
our genome.Thimerosal
Thimerosal is an organomercury compound which contains 50% mercury. It is
commonly used as an antiseptic agent, a preservative in vaccines, in skin tests
for allergies, eye drops, nasal sprays, tattoo inks, immunoglobulin preparations,
and many other products. It was patented in 1927 by a University of Maryland
chemist, Morris Kharasch, and was marketed by Eli Lilly as Merthiolate [47].
Thimerosal was first added into vaccines in 1940 as a preservative to prevent
contamination of multi‐dose vials by inhibiting the growth of harmful microbes
and fungus. Whenever a new needle is inserted into a vial it increases the chances
of that vial being contaminated by bacteria, which may cause serious infection.
This became apparent after two reported cases. One of the cases occurred in 1916
where four children died, and 60 others suffered from severe symptoms brought
on due to contamination of a typhoid vaccine with Staphylococcus aureus. The other
case occurred in Australia and claimed the lives of 12 out of 21 children who
received a diphtheria vaccine containing the same bacterium [47]. It is also used
in the preparation stages of some vaccines, for a similar purpose. Thimerosal via
vaccines became a major contributor of mercury exposure to children in the first
36 months of life, exposing these children to an amount of mercury beyond that
to be considered safe by guidelines [47,48]. Once metabolized by the body, thi-
merosal forms ethylmercury, which is bound to thiosalicylate [48]. We know that
the half‐life of ethylmercury is shorter than that of methylmercury, but that does
not discredit the fact that all forms of mercury can be harmful to the human body.
Organic mercury has a raised potential of harm compared with inorganic mercury
because organic mercury is a bio‐accumulator, meaning it has a tendency to accu-
mulate in the human body as it is absorbed by tissue and fat. Thimerosal‐ preserved
drugs have been proven to be a contributing factor in the long‐term accumulation
of the mercury‐body burden and can cause potentially harmful levels of mercury
in the human brain [49]. Methylmercury and ethylmercury distribute to all body
tissues, crossing the BBB and the placental barrier, and ethylmercury also moves
freely throughout the body [49–51]. Concerns based on extrapolations from
methylmercury caused thimerosal to be removed from US childhood vaccines,
starting in 1999. Since then, it has been found that ethylmercury is eliminated
from the body and the brain significantly faster than methylmercury, so the late
1990s risk assessments turned out to be overly conservative. Though inorganic
mercury metabolized from ethylmercury has a much longer half‐life in the brain,
at least 120 days, it appears to be much less toxic than the inorganic mercury