Another study has found no link between autism and the vaccine against measles, mumps and rubella (called the MMR vaccine). This time, the finding comes from a study of children at high risk of developing autism.
Although numerous studies have shown that vaccines do not cause autism, some parents still believe that vaccines and autism are related, and thus choose to not vaccinate their kids, researchers say.
In the new study, researchers examined health data and vaccination records of about 96,000 children who all had older siblings. The researchers found that there was no link between receiving the MMR vaccine and developing autism, even for the children who had an increased risk of autism because their older siblings had been diagnosed with the condition. Other studies have shown that having an older sibling with autism is a risk factor for developing the condition.
The researchers wanted to look at more data on the MMR vaccine and autism risk because "despite the research that shows no link between the MMR vaccine [and autism], parents continue to believe that the vaccine is contributing to autism," said study author Dr. Anjali Jain, of The Lewin Group, a health care consulting firm in Falls Church, Virginia. "Parents who already have a child with autism seem especially prone to this belief," Jain added.
Indeed, the researchers also found that the MMR vaccination rates were lower among the children whose older siblings had autism than among children whose older siblings did not have the condition. [Video: Why Vaccinate Your Child Against Measles?]
Although the new study did not examine the reasons for the difference in these MMR vaccination rates, previous surveys have shown that some parents who have a child with autism blame the vaccine for the condition, the researchers said. These parents may choose to not vaccinate their younger kids.
Still, the new study shows that, even in high-risk families, there is no increased risk of autism related to the MMR vaccine, said Dr. Thomas Frazier, director of Cleveland Clinic Center for Autism, who was not involved in the new study.
Many large studies have shown that the MMR vaccine does not cause autism. For example, in a review of studies published by the Cochrane Library in 2012, which included a total of nearly 15 million children, researchers found no relationship between the vaccine and autism.
In another review, published in 2014 in the journal Vaccine, researchers analyzed the results of previous studies that included more than 1.26 million children, and again found no link between the vaccine and autism. In a review of 67 studies, published in 2014 in the journal Pediatrics, the authors concluded, "There is strong evidence that the MMR vaccine is not associated with autism."
Frazier explained why some parents might believe that vaccines cause autism, despite the scientific evidence that shows otherwise. "Unfortunately, it is a psychological problem; it is not a data problem," Frazier told Live Science. "So we could probably do a hundred more of these studies, and you would not actually change parents' behavior."
One reason parents might believe there's a cause-and-effect relationship between vaccines and autism is that the onset of autism symptoms often coincides with the time when kids get vaccinated, Frazier said. However, "in reality, they just happen to occur at the same time in development," he said. Still, it is tough to get this type of correlation out if people's minds, he added.
Parents who fear vaccinations may choose to not vaccinate their kids based on the argument that they don't want to actively hurt their children, Frazier said. "I think this is the exact reason why the vaccination debate never goes away: It is because it is not about data; it is about fear," he said.
"And so [parents] end up opting for 'I am going to decline vaccination,' which, unfortunately, has led to the place where, actually, it is more common now to have these diseases," such as measles, that can be prevented through vaccination, Frazier added.
The study was published today (April 21) in the Journal of the American Medication Association.