If the thimerosal theory -- which holds the mercury-based compound once widely used in childhood vaccines responsible for at least some cases of autism and other problems -- starts to gain traction in court, and vaccine makers and government agencies are found liable for neurological damage to infants, the cost to the $6 billion-a-year industry could rival that of tobacco or asbestos litigation, some analysts believe.
An estimated 40 million American children were immunized in the 1990s, and, if current projections hold true, roughly 240,000 might get an autism diagnosis.
Thus far, more than 5,000 claims of thimerosal-related harm to children have been filed by parents in a special federal tribunal under the no-fault National Vaccine Injury Compensation Program.
The plan was created by the government in 1988 to prevent drug companies from fleeing the market, and endangering the immunization program, due to climbing liability costs.
That figure compares to 2,438 reports submitted in 2003 and 18 in 2001.
Since its inception, the program has paid more than $1.5 billion on about 1,900 complaints.
Several hundred similar claims were brought against vaccine makers, and others await trial in civil courts, although no plaintiffs' awards have been forthcoming thus far, said Charles Siegel, partner in Waters and Kraus in Dallas, the first U.S. law firm to file such a suit.
By now, the mercury-laced preservative has been phased out of vaccines administered in the United States to youngsters under 7. However, it still resides in certain booster -- notably tetanus and diphtheria -- and about half of flu shots.
The latter are advised for pregnant women and babies as young as six months under new, broadened Centers for Disease Control and Prevention guidelines, which stress the amount of mercury present falls well within levels the federal government considers safe.
The agency has declined to recommend that doctors select thimerosal-free shots for mothers-to-be and babies.
The only supplier for children younger than 2 -- Sanofi Pasteur -- has increased its capacity to make vaccines devoid of mercury, but because the government has expressed no preference, some of the capacity has gone unused, thimerosal opponents point out.
Largely at parents' goading to follow the lead of Japan and Europe, at least seven states -- California, New York, Illinois, Iowa, Missouri, Delaware and Washington -- have banned thimerosal from infant vaccines.
At least a dozen others have pending legislation to do so.
To critics' amazement and annoyance, pediatricians have vigorously protested such moves, viewing them as unnecessary, misguided, misleading and potentially dangerous if they frighten parents into refusing to immunize their children against diseases that once decimated young populations.
As these developments would suggest, rather than assuage apprehensions, the government's call in 1999 for removing thimerosal from childhood shots divvied up extra doses of doubt.
If the compound was so blameless, why would the government request and the pharmaceutical companies acquiesce to its banishment, albeit a partial one, critics asked.
And why, as the vaccine schedule expanded, did no one total up the new amounts of mercury children would receive as a result, an exercise in simple arithmetic that could have precluded the overdose the 1999 report unearthed, they wondered.
Their fears were fueled by such disquieting reports as an analysis of scientific literature on mercury toxicity led by Sallie Bernard, executive director of the parent-founded, thimerosal-opposing group SafeMinds (Sensible Action for Ending Mercury-Induced Neurological Disorders).
She and colleagues drew an alarming parallel of more than 100 characteristics and symptoms shared by autism and mercury poisoning.
Could it be that a toddler's social withdrawal, loss of speech, averted eye contact, insomnia, immune system upheavals, temper tantrums, seizures, unusual attachment to objects and routines and inexplicable repetitive behaviors, such as walking on tiptoes or flapping of hands, in fact resulted from the very strategies intended to protect him from harm, many parents and some physicians began to inquire.
Instead of wallowing in worry, thimerosal doubters set out to demand further analysis and action.
They made full use of the newfound tools of the Digital Age.
With instant worldwide communication at every computer user's fingertips, the messages of misgiving have spread speedily and widely.
They include diverse lists of suspects, from food allergies, pesticides and heavy metals to viral infections, antibiotics and other prescription drugs and, most emphatically, vaccines.
The vast majority of professionals -- including a veritable who's who of geneticists, epidemiologists, pediatricians, toxicologists, neuroscientists and statisticians -- and even many parents with autistic children find no scientific support for a causal link between vaccines and autism.
They have no doubt vaccines' potentially life-saving benefits outweigh any possible risks and warn of the danger of turning away from one of medicine's modern-day marvels.
Even in developed countries, when vaccine scares drive down the numbers of immunized children, once-silenced diseases roar back to life.
In Great Britain, for example, in the wake of the study implicating the MMR shot in autism, children's inoculation rates fell from 92 percent in 1995-1996 to 82 percent in 2002-2003, resulting in a measles outbreak.
Likewise, a drop in vaccination against whooping cough in 1974 was followed by an epidemic of more than 100,000 cases and 36 deaths in 1978.
In Japan, a plunge in whooping-cough vaccinations from 70 percent to 20-to-40 percent resulted in a leap from 393 cases and no deaths in 1974 to 13,000 cases and 41 deaths in 1979.
When two infants died in 1975 after receiving the pertussis shot, public fear soared, and the rates of Japanese children getting the inoculation sank to 40 percent. The following year the deadly disease went on a three-year rampage that killed more than 100 people and sickened 13,000 others.
U.S. health officials also express alarm over a raft of what they deem to be unproven, costly and potentially harmful treatments -- including strict diets, supplements and an increasingly popular heavy-metal-detoxifying technique called chelation -- that are being sold for thousands of dollars as a cure for mercury poisoning.
Next: Mainstream assurances fall on skeptical ears
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