Are Vaccines and Autism Related?

Today I will be discussing a recent news article about vaccinations and autism.  Also refer to the supplement.

I remember in 2008 reading an article about a British study that linked MMR vaccinations to autism; that study was published back in 1998.  The study caused wide-spread panic in Britain, and significantly decreased the proportion of immunized children.

Since then, the study has been widely discredited (other studies between 1998 and 2004 couldn’t find an association), and the British doctor responsible for the study was banned in 2010 for “professional misconduct” and ethic violations in his study.  However, the effects of his study still exist.

Whether vaccines cause autism is still a debated issue.  On Tuesday, MedicalNewsToday published an article about a study that addresses that exact debate.

The study was conducted on 1,008 vaccinated children and sought to examine any association between exposure to thimerosal (mercury) in vaccines and developing Autism Spectrum Disorder (ASD).  The study is set-up as a case-control study and split the children into two groups: “diagnosed with ASD” and “not having ASD.”  The researchers controlled for factors like age and gender.  Then, the study examined each child’s exposure to thimerosal in vaccines; they assessed exposures by looking at medical records and interviewing families (ensuring that book groups were assessed similarly).

The researchers found no association between thimerosal exposure and developing ASD.  In fact, the article says that the children without ASD generally had higher mercury exposures than children with ASD.  Additionally, the article reports that the study found that in babies, more vaccination with thimerosal-containing vaccines seemed to associate with less likelihood of developing ASD.

Even though the study adds to a growing list of studies that disprove the speculated vaccine-autism link, we have to read the article carefully.  Several questions have to be asked before we can say this study is really adequate.  How did the researchers calculate exposure?  One way would be to determine how much mercury was in each reported vaccine.  What is the odds ratio (OR)?  Without the OR, we cannot come to a conclusion for ourselves.

We also have to examine the weaknesses of any case-control study.  Case-control studies can suffer from biases like recall bias, though this study seemed to take care of that by cross-referencing family interviews with medical records.  Another bias is in the selection of the control and cases groups.  If the groups are not representative of their respective populations, then selection bias could be in play and the study cannot be extrapolated.

However, there are also strengths to a case-control study.  These studies are usually quick, cheap and efficient.  Plus, in comparison with randomized clinical trials, there are less ethical issues.

Regardless of the design and conclusions of this study, the vaccine-autism debate is still a public health issue.  The article reports that “one in every four parents is afraid of vaccinating their children because of a perceived autism risk.”  As long as that perception is still wide spread, the purpose of vaccinations will be undermined.  Therefore, it is important to assess the actual risk (through determining associations) and change perceptions with data.  However, it is still perplexing that such a wide spread fear still exists.  Why? would be an interesting question to answer.

Any speculations?
Eric