A major study published in one of the world’s leading medical journals has concluded that there is no link between the MMR (measles, mumps and rubella) vaccination and autism in children.

The findings from the study of a cohort of around 95,000 children will not surprise most scientists, who have been reassuring parents of the jab’s safety for 17 years, since the publication of now discredited research by the gastroenterologist Andrew Wakefield.

But the belief that autism and vaccinations are linked continues to cause many parents to decide against having their children immunised. As a result there have been avoidable measles outbreaks, including one in the US last year, which began in Disneyland in California in December and led to school closures and quarantine measures. In all, 159 children were diagnosed with measles across 18 states. The repercussions continue, as US doctors attempt to bring in legislation to prevent parents opting out of vaccination for their children on the grounds of “personal belief”, while activists accuse scientists of being in the pockets of drug companies.

The study is published in the Journal of the American Medical Association (Jama). It sought to find out whether children who had older siblings with autism and therefore were at higher risk than most, were more likely to develop an autistic spectrum disorder themselves after having the MMR jab. They found no association between the jab and autism, even among the high-risk children, and regardless of whether they had just the first shot, under the age of two, or the booster as well at around the age of five.

The study included anonymised data from 95,727 privately insured children from across the US, 2% of whom had an older sibling with an autistic spectrum disorder (ASD). The research team, led by Anjali Jain of the Lewin Group, Falls Church, Virginia, say that those families with a child already affected by autism may be less likely to have younger children vaccinated.

“Families with a child affected by ASD may be particularly concerned about reports linking MMR and ASD, despite the lack of evidence,” they write. “Surveys of parents who have children with ASD suggest that many believe the MMR vaccine was a contributing cause.”

Following up the children in the study, funded by US government institutions, the team found that 994 had been diagnosed with autism, with a higher proportion (6.9%) in the high-risk group with older siblings with ASD than among the majority (0.9%). But whether or not they had been given MMR vaccination did not make a difference.

“Controversy seems to follow autism like the tail on a kite,” says an editorial in the journal by Bryan H King of the University of Washington and Seattle children’s hospital. Since the 1950s, there have been disputes over what autism actually is and more recently there is the controversy over the rise in the number of children diagnosed with what is now classified as a spectrum disorder, he writes. Each new prevalence estimate amplifies the urgency to better understand causation.

The reluctance of some parents to vaccinate the younger siblings of children with the disorder could make it appear that there is less autism among children given the jab - not more, he says.

“Even so, short of arguing that MMR actually reduces the risk of ASD in those who were immunised by age two years, 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,” he writes.