Is autism correlated with vaccinations?
We now consider studies that attempt to find a difference in the autism rate between children who were vaccinated, and those who were not.
Reference 1 presents results of a British study, in which autistic children born since 1979 had their record of immunization checked to see whether they were immunized. The study found that
there was no difference within the margin of error in the likelihood that a child would develop autism. The risk ratio was 0·94 with a margin of error between 0·60 and 1·47.
there was no "step increase" in the autism rate when the MMR (measles, mumps, and rubella) vaccine was introduced.
This study is especially important - the original claim agains vaccines was that autistic symptoms were generated betwee 24 hours to 2 months after the administration of the MMR vaccine. This study shows the number of developing autism cases versus the time after birth, up to 150 months and longer. One can infer the following from the data:
There is a very similar distribution in both vaccinated and non-vaccinated children, as to the time when autistic symptoms are detected - typically between 18 months and 4 years.
The time (after birth) at which the MMR vaccine is given can be marked on this data - there is no evidence of increase in autism cases in the 1 day to 2 months interval after the vaccination (nor at any other time). If there was a connection, one would see a spike in the number of cases immediately following vaccination. (The same comment holds true for a second vaccination!).
The results in reference 2 come from a Danish study: all children born in Denmark between 1991 and 1998 were examined for their immunization record and autism. The risk ratio (the risk of autism, relative to the non-immunized group) was found to be 0.92, with a margin of error between 0.65 to 1.07.
Reference 3 provides results from a continuation of this Danish study. It specifically looks at the effect of the Thimerosal component of the vaccine. Thimerosal is an organic compound containing mercury, used since the 1930's as a preservative in vaccines, and suspected as a possible cause of autism. The study did not find any meaningful difference between autism rates children vaccinated with Thimerosal containing vaccines, and children vaccinated with vaccines devoid of Timerosal. The risk ratio for children vaccinated with Thimerosal (compared to childern vaccinated without Thimerosal) is 0.85, with a margin of error between 0.60 and 1.20.
Reference 4 presents an even more comprehensive British study. It examined all people born in 1973 or later, who had a first recorded diagnosis of a dvelopmental disorder between 1987 and 2001. Those who were vaccinated had a risk ratio of 0.86, with a margin of error between 0.68 and 1.09, relative to children who were not vaccinated.
Summarizing this part, we note that all the results point to a possible small reduction in risk of autism, for children who were vaccinated! However, this reduction is not statistically significant, but certainly indicates the lack of any measurable risk associated with vaccination!
Another large U.S. study (reference 5) corroborates this conclusion.
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Last Modification - May 22, 2009