[Source: Wikipedia]
[Source: Wikipedia]
Despite the lack of scientific evidence to support it, many parents still believe vaccines can cause autism. A new study that should help assuage concerns shows that giving children multiple vaccines on the same day does not increase the risk for autism. How persuasive the study will be to doubting parents, however, is anybody's guess.

The principle behind vaccines is to expose the body to harmless amounts of infectious pathogens so that the immune system can “remember” it by developing the proper antibodies. One fear is that vaccines – particularly the common measles, mumps, and rubella vaccine (MMR) – put excessive strain on young immune systems and thus render the children vulnerable to autism. Thus, many parents choose to not follow the vaccine schedule recommended by the Center for Disease Control (CDC) and delay or refuse entirely vaccines for their children.

To test the idea that overburdening the immune system predisposes children to autism, researchers at the CDC’s Immunization Safety Office compared the vaccine schedules of children with autism spectrum disorder (ASD) and those without ASD. If high amounts of vaccines raise the risk of autism, then those who had received more vaccines over the first two years of life or multiple vaccines on a single day should show a higher risk for ASD.

Data was gathered from 1008 children – 256 with autism spectrum disorder (ASD) and 752 without. From their vaccine histories the researchers calculated the maximum amount of antigens – molecules that stimulate production of the antibodies by which the immune system “remembers” – that each child was exposed to while receiving their shots. They then split each group further based on how many antigens those children received over time – from birth to three months old, from birth to seven months, and from birth to two years. The researchers concluded that risk for autism was not affected by the amount of antigens the children were exposed to over any of the time periods. They also looked at maximum exposure cases when the children took multiple vaccines on a single day. Again, the amounts of antigen didn’t affect whether or not the child developed autism.

Jonas Salk's vaccine, introduced in 1955, eradicated polio, then thought the most frightening health problem. [Source: Wikipedia]
Jonas Salk's vaccine, introduced in 1955, eradicated polio, then thought the most frightening health problem. [Source: Wikipedia]
Further analysis considered whether taking more vaccines increased risk for regressive autism in which children appear normal before age 1 or 2 but then suddenly “regress” and lose language and social skills they previously possessed. Because of the timing of the disorder – developing about the time the child is finished taking all his/her vaccines – there’s a concern that this form of autism might be particularly related to vaccine exposure. But as with the larger analysis, no connection was seen between vaccine amount and regressive autism.

The researchers also point out that, while it is true that today’s children are taking more vaccines they’re actually being exposed to less antigens. Today’s vaccines subject them to an average of 315 different antigens designed to stimulate resistance against diseases such as mumps, measles and rubella. Vaccines given in the 1990s exposed children to antigens numbering in the thousands.

The study was published in the April 1 issue of the Journal of Pediatrics.

The fear surrounding vaccines can be traced to British surgeon Andrew Wakefield who published a study in 1998 that “showed” vaccines increase risk for autism. A panicked public responded with an 80 percent drop in vaccine rates as late as 2004. But an assessment performed in 2011 roundly discredited the study, calling it an “elaborate fraud” and accusing Wakefield of falsifying data to support his theory. Subsequently the original study was retracted – 10 out of the 12 co-authors of the study led the exodus – and Wakefield was stripped of his medical license. Accusations levied against the surgeon cited a lawsuit against the manufacturers of an MMR vaccine for which Wakefield was a consultant and for which he was compensated $750,000.

But the damage was done, and its lasting effects are still seen today. About one-third of parents in the US still believe vaccines can cause autism, and 1 in 10 parents delay giving their children vaccines or refuse to give it to them altogether.

The study further solidifies the consensus among healthcare officials that vaccines don't cause autism. A comprehensive review by the Institute of Medicine published in 2004 examined the possibility of a link between vaccines (specifically MMR vaccines) and autism, including vaccines containing thimerosal, a preservative high in mercury that had been used in vaccines since the 1930s but recently discontinued due to health concerns. After examining the medical literature, the review concluded that the “evidence favors rejection of a causal relationship between the MMR vaccine and autism.” The CDC, FDA, World Health Organization and the Institute of Medicine all strongly state that the data does not support a link between thimerosal and autism. And while the new study goes far in ruling out a link between vaccine amount and autism, most likely many parents will still require even more data before they're fully inoculated against their fears.

Peter Murray was born in Boston in 1973. He earned a PhD in neuroscience at the University of Maryland, Baltimore studying gene expression in the neocortex. Following his dissertation work he spent three years as a post-doctoral fellow at the same university studying brain mechanisms of pain and motor control. He completed a collection of short stories in 2010 and has been writing for Singularity Hub since March 2011.