The controversy surrounding the relationship of common childhood vaccines and autism has been raging for nearly two decades. However, the debate is comprised of about 10% science and 90% politics and media exposure. In the wake of the most recent revelation that Andrew Wakefield, MD, the original author of the 1998 article linking autism to MMR vaccinations falsified medical history on nearly all of the patients that comprised his study http://www.cnn.com/2011/HEALTH/01/05/autism.vaccines/index.html, many families are left to wonder if they can really trust any medical advice. The impact of Wakefield’s article has done egregious harm to the general health of children worldwide. While the article was ultimately retracted by the publishing journal and Wakefield himself was stripped of his medical license in May of 2010, many countries noticed a precipitous drop in childhood vaccinations in the past decade. Surges of measles outbreaks rose in the aftermath and the CDC reported that 90% of the outbreaks in th US of measles were in children not vaccinated.
In addition to the impact on general medical care for children, popular media sources were quick to raise concerns about the safety of childhood vaccines and the preservatives used in them. With the most recent revelation that the original data may have been fabricated, many parents wonder if there is any way to make a reasonable decision about vaccinations.
The Relationship Between Vaccines and Autism
There is some science that families can draw upon. Large scale epidemiology studies are available that shed light into the relationship of vaccines and autism. In my own practice, I tend to rely upon studies that track live births over long periods of time in several geographic regions. For example, the city of Yokohama, Japan decided to terminate their MMR vaccine program that ran from 1988 to 1993 and institute an alternative program. With the new system, the rates of vaccinations fell to under 2% of the population between 1993 and 1998. This rapid change provided an ideal model to study the rates of autism since essentially the MMR vaccination rate dropped to nothing. Results from the study indicated that autism rates rose dramatically during the 1993 to 1998 time frame and could obviously not be attributed to MMR vaccines (Honda, Shimizu & Rutter, 2005). Studies conducted in Denmark (Madsen et al., 2002) and the UK (Smeeth et al., 2004) also demonstrated no relationship between autism rates and MMR vaccinations.
The Connection Between Thimerosal And Autism
In the United States, concerns also have been raised about thimerosal, which was the mercury derivative that was used to preserve some vaccines. Possible links between that compound and autism have been raised in recent years. This compound was removed from most vaccines between 1999 and 2001 and thus the impact should result in a lowering of new autism diagnosis in subsequent years. However, a longitudinal study in California that tracked quarterly rates of new autism diagnosis from 1995 to 2007, revealed no decrease in rates of new diagnosis from that period. In fact increases in the diagnosis of autism were found (Schechter & Grether, 2008). This and other studies are major factors in the CDC’s policy on the safety of childhood vaccines.
However, there have been some findings that vaccines other than MMR might pose some slight risk. For example, a recent study evaluated the relative risk of the hepatitis B vaccine in children born prior to 1999 for increased rates of autism. Since the hepatitis B vaccine may have contained mercury in that time frame, the presence of that compound could not be ruled out as a contributing factor (however, mercury free studies have been conducted in other countries and no relationship between mercury and autism was found). Data indicated a 3-fold increase in the risk of autism for infants vaccinated in the first year of life compared to those vaccinated later or not at all. In addition, non-white children seemed to be at slightly higher risk than white children (Gallagher & Goodman, 2010). While this study could indicate increased risk for autism in children given hepatitis B vaccinations in the first year of life, it is worth noting that the prevalence of autism in this study was 1 in 500, which is far less than common findings from the CDC of 1 in 150. In addition, parental education and two-parent families were at decrease risk in this study, which raises questions as to how well these findings might generalize to the larger population.
In general, there has been very little evidence across numerous studies from multiple countries of a risk between childhood vaccines, thimerosal and autism. In addition, several countries have changed diagnostic criteria and practices that account for the increases in diagnosis. These include younger ages of diagnosis, inclusion of milder cases, use of standardize instruments, etc. In addition, states where additional funds or services are available to autistic children frequently show higher prevalence of the disorder. This implies that more mild cases may be diagnosed with autism more often in those states since they would qualify for services.
Ultimately, decisions on vaccinations are best made with open communication between parents and physicians. I encourage all families to ask for the same literature we clinicians use to inform our practice. I also think it makes sense to ask your doctor what they would do for their own children. I get my own children vaccinated.