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: MMR Vaccine, Thimerosal continued...
Most medical researchers argue that this is probably a coincidence: Autism
symptoms tend to become apparent around the same time that children are
scheduled to get routine vaccines.
Although there are two separate issues concerning vaccines and autism,
they're often lumped together. One has to do with the measles, mumps, and
rubella (MMR) vaccine; the other involves vaccines containing the chemical
preservative thimerosal, which
contains a form of mercury that has been suspected of causing autism and
has recently been removed from most vaccines.
The MMR scare started 10 years ago with a report published in The
Lancet that described the cases of eight children who, as their parents
recalled, developed autistic symptoms and digestive ailments shortly after
getting their first MMR dose. The researchers proposed that the vaccine might
trigger a previously unknown form of regressive autism. They suggested that
maybe the measles virus in the vaccine lodged in the intestine, causing some
kind of reaction that then affected the brain.
After that, experts studied whether the MMR vaccine could cause autism. To
do that, they looked for clues among kids who did and didn't get the
Since that initial finding, 14 studies including millions of children in
several countries consistently show no significant difference in autism rates
between children who got the MMR vaccine those who didn't.
The bottom line: It's very unlikely that the MMR causes autism, researchers
Vaccine-Autism Disconnect: Complex Science
A lot of the confusion comes from the complexity of the science involved in
the issue. "It's hard to communicate in a way that's unambiguously
clear," says Melinda Wharton, MD, deputy director of the CDC's National
Center for Immunization and Respiratory Diseases.
Scientists often hedge
about saying whether their findings prove or disprove anything. That's because
the scientific method proceeds by constantly modifying theories rather than
But those who take issue with the
scientific consensus that vaccines have very little to do with autism focus on
research that seems to support their opinions. In particular, they point to the
work done by Mark Geier, MD, PhD, a former researcher at the National
Institutes of Health, and his son, David Geier, whose studies did show a strong
link between autism and vaccines.
So who's right? An Institute of Medicine panel reviewed all of the evidence
on vaccines and autism in 2004. But the reviewers excluded the Geier studies,
finding them "uninterpretable." The AAP issued a statement explaining
how the Geiers were probably wrong, listing 15 critical errors or omissions in
just one of their studies.
Still, some activists believe that authorities are suppressing this evidence
because it's inconvenient, and the Geiers have never backed off from their
conclusions. But experts say the basic flaws of their studies are glaringly