Morris Kharasch, the inventor of thiomersal (later known by trade name Merthiolate), can rest easy knowing he won't be crucified any longer for causing autism in thousands of children who have received vaccines. 

Okay, that may have been an inflammatory opening sentence... 

The accusation that childhood vaccines have caused an increase in the rate of autism over the last 15 years has been, since I first heard about it, one of the most frustrating interpretations of scientific data by the lay community.  These accusations first began following a study by Andrew Wakefield in 1998, published in the British medical journal The Lancet.  If you're interested, here is the originally article for your reading pleasure.  Basically, it looked at 12 children with gastrointestinal symptoms and behavioral disorders (autism, encephalitis, and disintigrative psychosis).  The onset of these symptoms were linked to near the time the children received the MMR vaccine.  From this paper, many studies began investigating a potential link between the MMR vaccine, and autism.  None have found "scientific evidence" of such a link, meaning no data looking at autism rates and MMR vaccines has suggested the MMR vaccine causes autism.  There have, however, been a number of studies showing NO link between autism and MMR vaccines.  Most of these either show no difference in autism rates between vaccinated and unvaccinated populations which are otherwise matched in age and gender, or that those who have autism show no difference in pre- and post- vaccination diagnosis rates (ie, no link between when they got the vaccine and symptoms started). 

Autism is a developmental disorder, which generally effects a child from the beginning of their affected milestones, although there is a form which is marked by regression of previously gained developmental milestones.  Given the timing of the MMR vaccine (first dose at 12-15 months), and the progression of normal childhood development, it is very likely that the MMR vaccine occurs at a time when a child's lack of developmental milestones is first being noticed.  Additionally, it is also possible that the child is not recognized as "delayed" until they come to their doctor, who asks (or should ask...) a number of developmental questions. 

Point being, there is no evidence, despite a number of people trying very hard to prove it, that MMR causes, increases the risk of, or plays a role in the development of autism.  There are also a number of plausible explanations for why these things may be temporally related. 

Now, this is by no means the only scientific or medical idea that has ended with a lack of scientific evidence to support it.  It's part of the game of medical research: sometimes things don't pan out.  So why is this issue so frustrating to me?  Well, because it was made so public prematurely, that people have taken it upon themselves to crusade against vaccines, leading to outbreaks of measles, mumps, and rubella, which for those who forgot, can in fact be fatal diseases. 


Congenital Rubella



Measles

Not only did people stop vaccinating against measles, mumps, and rubella, but they stopped getting their children vaccinated against ANYTHING!  Of course, some children will have bad reactions to vaccines.  This is rare, and generally the reactions are not serious.  And some children, because of other medical problems, are not candidates for vaccines.  These children rely on healthy children to get vaccinated for their protection against disease!  For herd immunity to be effective (ie, immunity for everyone based on those that are actually immune), about 80% of the population must get be immune.  When parents were following the recommendation of their physicians and getting children vaccinated, this number was not an issue.  But it has become one.