50EVERYTHING SEEMED FINE when tiny Robyn White came bouncing into the world on Dec. 12, 1994. As parents do, Scott and Jasmin White of Oakville, Ont., began taking young Robyn for her routine vaccinations. But at the age of just eight months, shortly after her first hepatitis-B shot, Robyn's eyes became crossed, she started flapping her hands and staring into space, and her hearing became hypersensitive. She never developed language skills. Last spring, her family filed a class-action lawsuit, alleging their seven-year-old's inoculation caused her autism. The suit, believed to be the first of its kind in Canada, claims that a mercury-based preservative in the vaccine called thimerosal is responsible for Robyn's neurological damage. The Whites now take their daughter to Dr. Jeffrey Bradstreet, a Palm Bay, Fla.-based autism specialist who recently testified on mercury in vaccines before a U.S. congressional committee. "It's garbage to say there's a reason to have residual neurotoxicity in an injectable for a child," says Bradstreet. "It's not a necessary risk."

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Vaccines have saved countless lives, but now the lawsuits are proliferating

Did thimerosal cause Robyn's autism? Maybe, says Bradstreet, but he doesn't know for sure. The case will take years to unravel. The Whites, however, are an example of how public trust in vaccines is on the wane. In the U.S., a raft of lawsuits claim thimerosal causes autism, attention deficit hyperactivity disorder (ADHD) and speech or language delay. The challenge is to separate medical fact from voodoo science.

Where should parents turn? Anti-vaccination Web sites tell horror stories, but a study of 22 of them published in the Journal of the American Medical Association in July found their content is largely unsupported by peer-reviewed scientific literature. Thimerosal's critics, however, are relentless in associating the agent with an apparent rise in autism rates. There could be various explanations for higher numbers of autistic children, including other environmental factors or simply an improvement in doctors' ability to diagnose the condition. Still, some respected health authorities are questioning the wisdom of injecting a heavy metal like mercury into an infant with a developing nervous system.

Thimerosal is used to prevent fungal and bacterial growth in multi-dose vials of vaccine. It guards against contamination when pediatricians jab the same vial repeatedly to vaccinate one child after another. Single-dose vials would eliminate the need for thimerosal, but they would cost more. In Canada, thimerosal-free vaccines now exist for all routine infant inoculations. But that is no reassurance for parents of children vaccinated before the use of alternative preservatives. A hepatitis-B vaccine without thimerosal became available last year, but a similar vaccine for high-risk infants born to hep-B-infected mothers still contains the compound. The diphtheria-pertussis (whooping cough)-tetanus vaccine had it until the mid-1990s. It's still in vaccines for flu, in some for meningococcal disease and in a number of special formulations for pertussis only, for diphtheria and tetanus, and for diphtheria, tetanus and acellular pertussis.

In the United States, thimerosal-free versions of routine inoculations are also available, but untraceable quantities of several common vaccines containing the substance are still in circulation. In developing countries, there is no choice: even routine inoculations contain it. David Klein, the Vancouver lawyer seeking class-action status for Robyn White's case, suggests drug manufacturers switch to the available alternatives, "particularly when children are getting an ever-increasing number of vaccines."

Unquestionably, vaccines are one of the great medical breakthroughs of the past century. Until 1920, Canada had 12,000 cases of diphtheria annually, with 1,000 deaths. Now there are fewer than five cases a year, and no deaths. Dr. Joanne Embree, chairwoman of the Canadian Paediatric Society's infectious diseases and immunization committee, assures vaccine-wary parents that extremely small doses of thimerosal are not dangerous. "If you're worried about something that is roughly the equivalent of Elvis showing up at your doorstep, as opposed to the real risk of disease," says Embree, "then I get upset." In fact, no study has conclusively linked thimerosal-containing vaccines to neurodegeneration. Equally true, however, is that no one has studied the long-term effects of exposing children to low doses of a mercury compound that has been in use for almost 70 years.

This much is known: the human body breaks down thimerosal to form ethylmercury, a chemical cousin of methylmercury, about which more is known. In some studies, prenatal exposure to low doses of methylmercury has been associated with subtle neurodevelopmental abnormalities. In 1999, the U.S. Food and Drug Administration determined that under the recommended childhood immunization schedule, some infants risked exposure to cumulative doses of ethylmercury that exceeded some federal safety guidelines governing exposure to methylmercury. Furthermore, high doses of mercury compounds, including thimerosal, ethylmercury and methylmercury, are known to be kidney and nerve toxins. In July 1999, the American Academy of Pediatrics and the U.S. Public Health Service recommended removal of thimerosal from vaccines as soon as possible.

As public confidence eroded, the Institute of Medicine, which advises the U.S. government on public health, created an independent committee to review immunization safety. Its conclusion last October: don't give vaccines containing the preservative to infants, children or pregnant women, and do more research. "The evidence," it reported, "is inadequate to accept or reject a causal relationship between exposure to thimerosal from vaccines and the neurodevelopmental disorders of autism, ADHD and speech or language delay." Still, because such a connection was "biologically plausible," and because thimerosal has been administered in millions of doses, it should be used cautiously while research continues.

In May, Health Canada posted a report on its Web site noting that routine exposure to thimerosal in Canada has been eliminated. "As thimerosal-free vaccines come to market," said the report, "it is prudent for Canada to incorporate these products into immunization programs, to minimize to the extent possible the total burden of organic mercury exposure to children." In situations where a thimerosal-free alternative does not yet exist, the report recommended vaccination given the higher risk associated with disease.

Robyn White's lawsuit is at its earliest stage. Her father, Scott White, declined to be interviewed. Co-defendant Merck Frosst Canada & Co. had nothing to say, but a GlaxoSmithKline spokesman says the company "firmly believes there is an absence of reliable scientific evidence supporting the claim that harm is caused by pediatric vaccines containing thimerosal." A similar but separate suit against Aventis Pasteur Ltd., also filed by Klein in Vancouver, claims the firm's diphtheria-pertussis-tetanus vaccine caused autism in children inoculated in the '80s and '90s.