What is autism spectrum disorder?
Autism, or autism spectrum disorder, refers to a range of conditions characterized by challenges with social skills, repetitive behaviours, speech and nonverbal communication, as well as by unique strengths and differences. We now know that there is not one autism but many types, caused by different combinations of genetic and environmental influences.
Do Vaccines Cause Autism?
Autism rates in developing countries have risen remarkably in the past 20 years. For children born in 1992, according to the U.S. CDC, about 1 in 150 would be diagnosed with an autism spectrum disorder (ASD). For children born in 2004, about 1 in 68 children would receive an ASD diagnosis. It is difficult to compare autism rates from the 1990s and later with rates from the 1940s through the 1980s: in earlier years, autism was associated primarily with very severely affected individuals and the rate of autism was estimated to be only about 1 in 10,000 people. Beginning in the 1990s, our understanding of the spectrum of autism has expanded greatly, and now individuals who would most likely previously not have been thought of as having autism may be classified with one of a variety of ASDs.
One of these researchers was gastroenterologist Andrew Wakefield, MD, who went on to further study a possible link between the vaccine and bowel disease by speculating that persistent infection with vaccine virus caused disruption of the intestinal tissue that in turn led to bowel disease and neuropsychiatric disease (specifically, autism). Part of this hypothesis – that vaccination was associated with autism – had been suggested previously a few researchers. For example, Fudenberg, in a small pilot study published in a non-mainstream journal, posited this relationship, as did Gupta in a review of possible treatments for autism.
Overview of Vaccines & Autism
Vaccines are generally considered to be the most successful public health intervention ever devised. And yet there have been opponents of vaccines ever since there have been vaccines. So-called antivaccinationists have claimed over the years that vaccines do not work, despite the overwhelming evidence that they do. They often spread misinformation about the vaccine, such as the notion that vaccines weaken the immune system, when in fact they work by strengthening the immune response against the target infection.
In recent years the antivaccine movement has focused on the claim that vaccines are linked to neurological injury, and specifically to the neurological disorder autism, now referred to as autism spectrum disorder (ASD). However, the scientific evidence overwhelmingly shows no correlation between vaccines in general, the MMR vaccine specifically, or thimerosal (a mercury-based preservative) in vaccines with ASD or other neurodevelopmental disorders.
The primary argument made for an association between thimerosal and ASD is that the rate of diagnosis of ASD has been steadily increasing since the early 1990s. At that time also the routine vaccine schedule was increasing, resulting in an increasing total dose of thimerosal. The antivaccinationists then assume causation from correlation to blame rising ASD rates on thimerosal.
However, by 2002 thimerosal was completely removed from the routine vaccine schedule, and now remains only in some flu vaccines. The total dose of thimerosal exposure is far below 1990 levels before ASD diagnoses began to rise. Antivaccinationists predicted that ASD rates would fall dramatically in the years following the removal of thimerosal from most vaccines – but rates have continued to rise without even the slightest change in the rate of increase. This is a powerful refutation of the thimerosal-autism hypothesis and has been replicated in other countries.
Vaccines Don’t Cause Autism
The scientific evidence is overwhelming — there is no link between vaccines and autism. Most people are vaccinating their children on schedule, but the risk to the public is real even if just a few children are not vaccinated.
The “anti-vax” movement lost all credibility in 2005 when The Lancet fully retracted the paper that first suggested a link between vaccines and autism after its findings were debunked. In 2010, the study’s lead author and figurehead of the anti-vax movement, Andrew Wakefield, was further accused of fraud, ethical violations and scientific misrepresentation, and his license to practice medicine was revoked in the United Kingdom.
Since Wakefield’s study was published in 1998, extensive scientific literature has amassed debunking any associations between vaccines and autism. For example, in 2012, an analysis of 10 independent studies including more than 1.26 million children found no relationship between autism and vaccination in general or the MMR vaccine specifically. This same study also found no link between autism and mercury or thimerosal – a mercury-based preservative that was removed from all childhood vaccines in the United States in 2001 due to now-disproven concerns that it might be harmful to children.
Fortunately, many people understand the importance of herd immunity to protect those who are too young or infirm to be vaccinated. Last year, the American Academy of Pediatrics changed its policy to permit doctors to refuse to treat children whose parents won’t vaccinate them. Many parents who care about their children’s health are demanding that “anti-vaxxers” not put other people’s children at risk and are calling for an end to religious and philosophical immunization exemptions.
Most scientific and medical experts are satisfied that no connection exists between vaccines and autism and other neurodevelopmental disorders. Still, critics continue to question the issue. Researchers continue to examine these questions, but there is no evidence that these factors play a role in autism development. Most autism researchers hold that the causes of autism are many and include genetic and environmental factors, but do not involve vaccines.