Is there a link between autism and childhood vaccines ?

The National Vaccine Advisory Committee has recommended that new studies be done to evaluate vaccine safety, including additional study of the potential vaccine-autism link.  We have learned a great deal about autism in the past decade or so. There is a genetic component to autism, yet it is not from a single gene. Autism and autism spectrum disorder are called "polygenic" diseases, meaning that multiple genes have been shown to be associated with these diseases.

Studies have also clearly shown that there is an environmental component, i.e., "a trigger", that is required. What this means is that some children have a genetic predisposition so that when they experience some stress or damage they develop autism, while children without this genetic predisposition who are exposed to the same stress or damage do not develop autism. Vaccines are an obvious potential environmental trigger for autism.

Childhood vaccination programs were introduced to the US about 1970. Before this we didn't vaccinate our children widely, because vaccines other than smallpox and polio, were not available. Between 1970 & 1985
about 60% of US children were vaccinated for mumps, measles and rubella (MMR). Nationwide vaccination campaigns brought that rate up to over 90% by the mid-1990's. 

In 1979 a new version of the MMR vaccine was introduced to the US, and by 1983 only the new version was available. At the same time, autism began rising in the US after 1979 and spiked up dramatically between 1983 and 1990 from 1 in 10,000 children to 1 in 500.  Autism cannot usually be diagnosed until a child is at least 3 years old, so the gap between the 1979 introduction of the new vaccine and the 1983 first spike in autism diagnosis is compelling.  In 1988, this new version of the MMR vaccine used in the US was also introduced to the UK. Autism then spiked up dramatically in the UK. 

The association between the introduction of the new MMR vaccine and autism rates, separated by a decade
in the US and the UK, was what led scientists to first suspect that vaccines, particularly the new MMR vaccine, might be associated with autism. Studies done to examine potential links between vaccines and autism have focused on the measles virus in this new MMR vaccine and on the presence of mercury (Thimerosal) in vaccines.
However, in some countries mercury was completely removed from vaccines as early as 1993, yet autism rates have continued to increase in those countries.  The scientific community has done careful, detailed studies that indicate mercury in vaccines is not a trigger for autism.

While the pharmaceutical industry would like to conclude that vaccines are not the environmental trigger for autism, the association between the new vaccine versions and autism is too compelling for parents and grandparents to ignore, and real-life experience continues to implicate vaccines as a trigger for autism in some way.  But what is in the vaccines that could be a trigger for autism?

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