After assuring parents that additives in vaccines don’t cause brain damage, scientists have found what they believe could be a “smoking gun” linking these additives to autism and attention-deficit hyperactivity disorder in children.
In a study published online today, two months ahead of its scheduled release in the journal Molecular Psychiatry, U.S. researchers have discovered an apparent link between thimerosal, a controversial mercury-based preservative once commonly used in childhood vaccines, to an increased risk of neurological disorders such as autism and ADHD.
While most vaccines used in Canada have been thimerosal-free since the early 1960s, the preservative was used in the annual flu shot doctors recommended this year for even healthy children.
In tests on human brain cells, researchers found two natural chemicals — one compound that stimulates cell growth and dopamine, which transmits nerve signals — are both key to a process in the brain called methylation. Methylation helps DNA work properly and is crucial to the normal development of the brain. The team found thimerosal, ethanol, and the metals lead and mercury, all interfere with methylation.
What’s more, researchers found that thimerosal interfered with methylation even at doses 100 times lower than a child would receive after a shot with a vaccine containing the preservative.
“It was by far the most potent,” says investigator Richard Deth, a professor of pharmacology at Northeastern University in Boston.
He said the study, which also involved researchers from Johns Hopkins University, the University of Nebraska and Tufts University in Boston, could account for the rising rates of autism since the early 1980s, when more thimerosal-containing shots were added to a child’s vaccine schedule.
A recent review of vaccine-related “adverse events” in the U.S. found a “significant correlation” between shots containing thimerosal and autism, the researchers report.
In a press release, the journal said the new study is “the first to offer an explanation for possible causes of two increasingly common childhood neurological disorders.”
But one of Canada’s leading experts in vaccination says large studies have repeatedly failed to find any association between brain damage and vaccines that do, or don’t, contain thimerosal.
“What (the researchers) are doing in the test tube may or may not have any relationship to what happens in the body,” added Dr. Ronald Gold, professor emeritus of pediatrics at the University of Toronto and author of Your Child’s Best Shot: A Parent’s Guide to Vaccination. He says there’s no evidence that the low doses of thimerosal researchers tested would even cross a child’s blood-brain barrier.
But Deth thinks there may be a link, and he believes thimerosal may play a role for the one out of 200 children who will experience some kind of developmental disorder.
Before the early ’90s, most causes of autism were believed to have a strong genetic component, and symptoms surfaced soon after the child was born.
But with a newer and more common form of the disease, known as regressive autism, children appear to be developing normally but then suddenly regress.
“They lose functions they had before, such as early speech,” Deth says. “Parental anecdotes and clinical reports have suggested it happened during periods of high vaccine exposure.
“Up to now, people have said the cause, or causes, of autism, are unknown. Our work isn’t final in any sense at all, but it seems to point to this biochemistry as a potential, or even primary, cause of autism.”
Thimerosal had been used to prevent the growth of bacteria or fungi in multi-dose units of vaccines for diseases such as hepatitis and diphtheria, pertussis (whooping cough) and tetanus, or DPT. Ontario, Nova Scotia, Newfoundland and Prince Edward Island have not used childhood vaccines containing thimerosal since the early 1960s. All other provinces began to move to thimerosal-free vaccines starting in 1997. As of March 2001, vaccines for routine immunization of children in Canada have been available without thimerosal.
But the annual flu shot which Canadian doctors this year began pushing on even healthy children over six months of age contains the preservative. And thimerosal is still found in larger, multi-dose vaccines shipped to Third World countries.
Dr. Laszlo Palkonyay, medical-scientific adviser for Quebec-based flu vaccine maker Shire Biologics, said a study published in the journal Pediatrics last September, which was based on a registry of all psychiatric admissions in Denmark between 1971 and 2000, found no trend toward an increase in autism rates during the period thimerosal was used in vaccines in that country. In fact, he said the incidence of autism increased after the preservative was removed from vaccines in 1990.
Deth believes it is more than coincidental that his team’s work “falls directly in line” with some current treatments for autism. For example, his group found that thimerosal inhibits the body’s ability to break down a form of vitamin B12, which doctors are now using, with some success, to treat autistic children.
Groups such as the B.C.-based Vaccination Risk Awareness Network have heard from parents convinced routine childhood vaccines sickened or killed their children, and class action lawsuits blaming vaccines for deaths and disorders such as autism have been filed in the U.S. and Canada.
Deth stressed that more work needs to be done, and that there are other risk factors for autism, such as genetic factors and other possible environmental exposures. “Some would consider (thimerosal) a smoking gun,” Deth said. “I think it is.”