Autism-Vaccine Link: Evidence Doesn't Dispel Doubts
Many major medical groups say vaccines don't cause autism. Many parents say they do. So who's right?
Vaccine-Autism Disconnect: The Mercury Question
As if the MMR vaccine wasn't enough of a hot potato, other vaccines also caused concern.
When researchers started looking for a possible link between autism and the MMR, all other childhood vaccines came under scrutiny, too. In 1998, 30 different vaccines with thimerosal in them were given to children. U.S. public health officials realized that the recommended schedule of vaccines could give some children mercury that exceeded the limit considered safe by government standards.
In 1999, the U.S. Public Health Service and the AAP asked vaccine makers to reduce or remove thimerosal in vaccines. By 2001, all routine childhood vaccines were available thimerosal-free.
The 2004 IOM review included five large-scale studies that compared autism rates in vaccinated and unvaccinated children. These and other recent studies, including one published in TheNew England Journal of Medicine in September 2007, have shown that children who received vaccines with thimerosal are not more likely to have been diagnosed with autism than those that weren't vaccinated or received less thimerosal from vaccines.
Sallie Bernard, founder of the advocacy group Safe Minds, tells WebMD that she doesn't believe the results of epidemiological studies showing no link between autism and vaccines. "We say you have to look at the biology," she says.
In her opinion, mercury poisoning and autism seem too much alike to rule out mercury as a cause. Mercury poisoning can cause brain damage, and symptoms can be similar to those of autism.
"I certainly wouldn't argue that the only source of mercury and the only source of harm is the mercury in vaccines," Bernard says. She says she believes children continue to be harmed by vaccines that still contain thimerosal.
But while Harvard's McCormick agrees that mercury is a dangerous substance, the claim that mercury poisoning and autism are the same doesn't hold up under scrutiny, she says. "It's based on a very superficial similarity."
Symptoms of mercury poisoning can include irritability, depression, anxiety, visual problems, speech problems, and sensory nerve problems. In autism, there can be findings of delayed speech, increase or decrease in response to sensory stimuli, and avoidance of human eye contact.