Responding to the reader:
Is there a link between vaccinations and autism?
Autism expert Dr. Lonnie Zwaigenbaum addresses the persistent rumours.
About this feature
AHFMR frequently receives letters requesting information about Heritage research or about various medical conditions. "Responding to the reader" is an AHFMR Research News feature intended to provide up-to-date information related to readers' questions, with the help of experts in the Alberta research community. AHFMR cannot provide medical advice, however; please consult your family physician about your specific health concerns.
If you are the parent of a young child, you may have had second thoughts when taking your toddler in to the doctor for a routine vaccination. You may have been wondering about the rumours that have been circulating for a number of years that this vaccine could cause autism in your child. But the evidence is in: There is no link, and the rumours should be laid to rest.
Autism is thought to develop before birth, but usually, autistic children don't start to show atypical behaviour until they are 12 to 18 months of age-right around the time that many children receive their childhood vaccinations-and their parents can't help putting two and two together.
AHFMR Scholar Dr. Lonnie Zwaigenbaum (see the story on his research ), who holds an endowed chair in autism research through the Stollery Foundation , explains the confusion. "The concern is there because I think that there truly are families who notice the initial signs of autism shortly after vaccination. However, studies have clearly shown that rates of autism are similar in vaccinated and non-vaccinated children; and that, among children with autism in these two groups, the timing and the pattern of onset is very similar."
In 1998 a study by British gastroenterologist Dr. Andrew Wakefield and a group of colleagues heightened concern around this issue by claiming that there was a link between the MMR (mumps, measles, rubella) vaccine and autism. Because the study was published in a prestigious medical journal, and because it generated significant public debate, the claims have remained credible in the minds of the public.
Years of subsequent research have failed to uphold Wakefield's conclusion. In fact, in 2004-six years after publication-10 of the 12 people who contributed to the original study retracted its claims on the basis of insufficient data. Dr. Zwaigenbaum understands, however, why the rumours still persist.
"What's compelling to a scientist, in terms of large sample sizes, may be less compelling to a family. A family wants to know more at an individual level: Is there a possibility that the vaccine might increase risk? Personal stories can be more powerful than large population-based research studies," he explains.
But how do these large population-based studies work? To test if a link exists between a certain vaccination and autism, one need only find out whether there is a higher rate of autism in the segment of the population that received the vaccination than there is in the segment of the population that did not. Dr. Zwaigenbaum describes a New England Journal of Medicine article that compared 400,000 children who were vaccinated with 100,000 who were not. The groups showed equal rates of autism. So something else must be underlying the development of the disorder.
Other concerns centre around the use of a vaccine preservative called thimerosal and the incidence of autism. Information gathered by the Department of Public Health in California refutes this connection. Statistics covering the period from 1995 to 2007 show that rates of autism continued to increase even after thimerosal was phased out of vaccines in 2001.
If vaccines can be discounted as a cause of autism, what factors are relevant? Dr. Zwaigenbaum points out that genetic influences play a strong role in the development of autism, although no single "autism gene" has been identified to date. "There's emerging evidence that specific genes that are involved in the risk of autism seem to play a role in brain development," he explains.
So how would Dr. Zwaigenbaum respond to parents wondering whether or not to vaccinate their child? He would respond with sympathy and understanding, but in firm support of the scientific consensus. "As a pediatrician, I'd certainly recommend vaccination, but I also respect that there's a lot of information out there that parents are processing. I think that our role is to help parents make informed decisions, but also encourage healthy practices such as vaccination."