Do Vaccines Cause Autism?

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Scientists who look at the question in different ways come up with the same answer.

GIVE THE SHORT--OR NOT? That decision worries parents who have heard of a possible connection between childhood immunizations and autism.

The concern has focused on the measles-mumps-rubella (MMR) vaccine and thimerosal, a preservative once used in a number of vaccines. But many studies have been completed since the link was first proposed, and their results are reassuring. In the overwhelming majority of cases, it seems the connection is more apparent than real: Affected children simply receive the vaccine around the time their disorder is recognized.

Epidemiologists have tackled the question en masse. For instance, researchers in Denmark studied immunization records and autism diagnoses for every child born in that country between 1991 and 1998, and found that unvaccinated children were just as likely to be diagnosed with autism as those who had gotten the shots. Evidence also points away from thimerosal: In Denmark and Sweden, autism diagnoses have continued to climb for as many as 6 years after the chemical was eliminated from all childhood vaccines.

Other research shows that signs of autism can appear well before a child is old enough for the first MMR shot. By studying home videos of children later diagnosed with autism, psychologist Geraldine Dawson, Ph.D., of the University of Washington, has detected autistic behavior in babies as young as 8 months (the first MMR shot is generally given between ages 12 and 18 months). At bath time, mealtime, or first-birthday parties, Dawson says, these children fail to make eye contact with others, don't look at what others are pointing to, and don't turn their heads when parents call their names. "We seem to come into the world wired to know that people are special and to want to capture their attention. In autistic babies, this [capability] seems not to be there," Dawson says.

Neuroscientist Eric Courchesne, Ph.D., of the University of California, San Diego, has demonstrated that brain growth in autistic children may go awry shortly after birth. In his study, the heads of youngsters who were later diagnosed with autism began to grow at an abnormally fast rate at about 2 months of age. Brain scans showed that the overgrowth is concentrated in areas of the brain that go to work when a person perceives and understands facial expressions, deciphers emotions, and interprets tone of voice. These are abilities that autistic children profoundly lack.

"At the moment that babies ordinarily begin to learn these very important skills, their brains are clouded by this sudden overgrowth," Courchesne says. "Because this growth process likely begins at birth or soon after, we have to look at an earlier time flame than vaccines to find what's responsible."

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By Kathleen M. Wong

Kathleen M. Wong is senior editor of California Wild magazine.

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