Another study finds no link between MMR vaccine and autism
Angela Mulholland, CTVNews.ca
Published Wednesday, April 22, 2015 11:09AM EDT
Last Updated Wednesday, April 22, 2015 6:35PM EDT
Another scientific study has added to what has become a mountain of evidence that there is no link between autism and the vaccine that prevents measles, mumps and rubella (MMR).
These latest findings are based on a study of 95,000 U.S. children. Among the kids, approximately two per cent had an older sibling diagnosed with autism spectrum disorder (ASD).
The researchers wanted to know whether there was any link between the vaccine and autism risk, as well as whether the younger siblings, who are already considered at higher risk of autism because of their genetics, would have an even higher risk of autism if they received the MMR vaccine.
The team found that 6.9 per cent of the kids with older siblings with autism went on to be diagnosed with autism, compared to just 0.9 per cent of the rest of the group. But whether they had been received the MMR vaccination did not make a difference, the researchers write in the Journal of the American Medical Association.
"Consistent with studies in other populations, we observed no association between MMR vaccination and increased ASD risk among privately insured children," wrote the authors, led by endocrinologist Dr. Anjali Jain.
"We also found no evidence that receipt of either one or two doses of MMR vaccination was associated with an increased risk of ASD among children who had older siblings with ASD."
Although there have been several studies over the last 15 years refuting links between the MMR vaccine and autism, many parents continue to associate the two. Surveys of parents who have children with autism suggest many believe the MMR vaccine was a contributing cause.
This belief often prompts parents to avoid vaccinating their younger children or to delay vaccination, which puts their kids at risk of contracting the vaccine-preventable diseases.
This study found that the MMR vaccination rate for the children with unaffected siblings was 92 per cent by age five. But the vaccination rates for kids with older siblings with autism were only 86 per cent at age five.
The analysis found that the MMR vaccine was not associated with an increased risk of ASD at any age. In fact, the largest risk factor was simply having an older sibling with autism.
An accompanying editorial by Dr. Bryan King, from the Seattle Children's Hospital, said it is clear there is no vaccine-autism link.
"The only conclusion that can be drawn from the study is that there is no signal to suggest a relationship between MMR and the development of autism in children with or without a sibling who has autism," King wrote.
"Taken together, some dozen studies have now shown that the age of onset of ASD does not differ between vaccinated and unvaccinated children, the severity or course of ASD does not differ between vaccinated and unvaccinated children, and now the risk of ASD recurrence in families does not differ between vaccinated and unvaccinated children."
Dr. Shelani Desai, a medical epidemiologist with Ontario Public Health, says it's not clear why some still hold onto the belief that vaccines increase the risk of autism.
She notes the 1998 study by Andrew Wakefield that purported to find a link between the MMR vaccine and autism did garner a lot of media attention at the time which was further propelled by actress Jenny McCarthy.
"I think most parents don't know that that study was revoked from the journal it was published in," she told CTV News Channel Wednesday.
"They may not know that there have been over a dozen studies that found no link between MMR vaccine and ASD."