Extensive investigation into vaccines and autism spectrum disorder has shown that there is no relationship between the two, causal or otherwise, and that vaccine ingredients do not cause autism. Major health authorities, including the World Health Organization, the National Health Service, the Centers for Disease Control and Prevention and the United States Food and Drug Administration, along with large-scale epidemiological research, reinforce the scientific consensus that vaccines are safe, that multiple concurrent vaccinations do not overwhelm the immune system, and that autism cannot be attributed to vaccination. Scientist Peter Hotez researched the growth of the false claim and concluded that its spread originated with Andrew Wakefield's fraudulent 1998 paper, and that no prior paper supports a link. Despite the scientific consensus for the absence of a relationship, and the Wakefield paper's retraction, the anti-vaccination movement at large continues to promote theories linking the two. Celebrity endorsements, social media campaigns and selective reporting have fuelled the anti-vaccination movement and public misunderstanding of vaccines. Fringe political actions continue to promote debunked claims. A developing tactic appears to be citing irrelevant or dubious studies to support a questionable claim.
Claimed mechanisms
The claimed mechanisms have changed over time, in response to evidence refuting each in turn. Anti-vaccine groups claim that specific vaccine ingredients can cause autism. Some of the most frequently mentioned ones are thiomersal, aluminium adjuvants and formaldehyde.
MMR vaccine
The idea of a link between the MMR vaccine and autism came to prominence after the publication of a paper by Andrew Wakefield and others in The Lancet in 1998. This paper, which was retracted in 2010 and whose publication led to Wakefield being struck off the British medical register, has been described as "the most damaging medical hoax of the last 100 years". Wakefield's primary claim was that he had isolated evidence of vaccine-strain measles virus RNA in the intestines of autistic children, leading to a condition he termed autistic enterocolitis (a condition never recognised or adopted by the scientific community). This finding was later shown to be due to errors made by the laboratory where the polymerase chain reaction (PCR) tests were performed. In 2009 The Sunday Times reported that Wakefield had manipulated patient data and misreported results in his 1998 paper, thus falsifying a link with autism. A 2011 article in the British Medical Journal describes the way in which Wakefield manipulated the data in his study in order to arrive at his predetermined conclusion. An accompanying editorial in the same journal described Wakefield's work as an "elaborate fraud" which led to lower vaccination rates, putting hundreds of thousands of children at risk and diverting funding and other resources from research into the true cause of autism. On 12 February 2009 a special court convened in the United States to review claims under its National Vaccine Injury Compensation Program ruled that parents of autistic children are not entitled to compensation in their contention that certain vaccines caused their children to develop autism. The Centers for Disease Control and Prevention (CDC), the IOM of the United States National Academy of Sciences, and the National Health Service have all concluded that there is no link between the MMR vaccine and autism. A systematic review by the Cochrane Library concluded that there is no credible link between the MMR vaccine and autism, that the MMR vaccine has prevented diseases that still carry a heavy burden of death and complications, that the lack of confidence in the MMR vaccine has damaged public health, and that the design and reporting of safety outcomes in MMR vaccine studies are largely inadequate. Further, an epidemiology study concluded that even children labelled high risk for autism, due to an older autistic sibling, that received the MMR vaccine resulted in no causal connection between the vaccine and autism or the increased risk of being diagnosed with autism. The assumption that MMR vaccines cause autism is not isolated to the United States. A seven-year study was done in Denmark from 1991 to 1998 following children who received the MMR vaccine. The results of the study found that when comparing the vaccinated children to the unvaccinated children, the risk of autism in the vaccinated group was 0.92. Also, the risk of another autism disorder was 0.83. The study concluded there was no association between the MMR vaccine and autism. The result held even when exploring the age of the child when the vaccine was given, the vaccination date, or the amount of time after the vaccine.
Thiomersal
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