New Intensity to Debate Over Autism Cause
Parents and Researchers Grapple With Claims That Autism Is Linked to Thimerosal in Vaccines
WebMD News Archive
One of the heartbreaking peculiarities of autism is that a child will seem
to be developing normally. Then, suddenly, at age 2 to 4, everything seems to
That's just when kids are getting their vaccinations. To many parents, a
vaccine/autism link seems obvious. Until very recently, many parents believed
the problem was with the measles/mumps/rubella vaccine. Although many people
still cling to this idea, most have come to reject it.
But until recently, many other vaccines contained a mercury-based
preservative called thimerosal. Vaccines used to get contaminated with germs.
Those germs killed kids. So drug companies used thimerosal to save lives. It
Oddly -- for a substance given to nearly every child in the U.S. -- nobody
really knew much about thimerosal.
Even now, says toxicologist Thomas Burbacher, PhD, very little is known.
Burbacher is associate professor of environmental and occupational health
sciences and director of the infant primate research lab at the National
Primate Research Center, University of Washington.
"It is incredible so many millions of kids have been vaccinated with
this compound with so little data on it," Burbacher tells WebMD. "But
line it up with everything else. A lot of information is missing on a lot of
compounds in daily use. And a lot of people thought the amount the kids were
getting was so small, it was not a priority."
The Thimerosal Debate and the EPA
Thimerosal is 49% ethyl mercury. A closely related form of mercury, methyl
mercury, is a known toxin. Since nothing was known about thimerosal, safety
measures were based on what was known about methyl mercury. Everybody thought
that thimerosal would be safe if the doses given to kids were below the toxic
dose for methyl mercury.
But three things happened. One was that kids started getting more and more
vaccines containing thimerosal. Meanwhile, the U.S. Environmental Protection
Agency got new information and lowered what it considered to be a toxic dose of
"In the 1990s, those two lines merged," Burbacher says. "Someone
at the FDA noted that when you add all the vaccines up they totaled more than
the new EPA standard for methyl mercury. So then the other thing that occurred,
during that same time period, was an increase in rates of autism