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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: Complex Science continued...

Marie McCormick, MD, a professor at the Harvard School of Public Health, oversaw the committee that conducted the 2004 IOM vaccine safety review and extensively reviewed their work. To begin with, she says, the Geirs used inappropriate data sources for their studies.

One study was based upon case reports in the CDC's system for tracking vaccine side effects. Those reports can alert researchers to issues that deserve study. But they're a far cry from the sort of evidence scientists need to prove something.

In addition, when researchers try to prove cause and effect, they use samples that reflect the general population. So using only data about people who got sick from vaccines isn't generalizable.

Other studies done by the Geiers also had flaws, McCormick says. In one of them, the Geiers estimated a rate of autism in different groups of U.S. children based upon case records for government-sponsored special education programs. But because eligibility requirements vary from state to state, it's unlikely that the special-ed rolls accurately reflect a real rate of autism.

What's more, the Geiers made major errors with their calculations. "They didn't understand how to analyze the data," McCormick says. Such statistical flaws are fatal, but all that goes over the heads of many people. "If you stand up in front of an audience and explain that, you are going to look like a nerd," McCormick says.

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.

Next Article:

Would the fear of autism keep you from getting your child vaccinated?