Vaccine sceptics appear to be swaying many parents of children with autism to forgo critical childhood vaccines, a new study suggests.
This includes the hesitation to fully immunise includes the children's younger siblings, whether or not they suffer from autism , the researchers added.
Western anti-immunisation movements have also taken root in South African communities resulting in some parents refusing to vaccinate their children. Nearly a third of South African children are not vaccinated.
This means that "children with autism spectrum disorder, and their siblings, may be at greater risk of vaccine-preventable diseases," said study author Ousseny Zerbo. He is a postdoctoral fellow at the Kaiser Permanente Vaccine Study Center at KP Northern California, in Oakland.
But the greater risk doesn't stop there, due to a concept called “herd immunity”.
"In order to disrupt the chains of infection in a population, a large portion of the population needs to be immune to the infection," Dr Zerbo explained. "A higher vaccination rate can break those chains of infection. This is why it is important for a large proportion of the population to be vaccinated."
And despite the fact that anti-vaxxers believe there is a link between childhood vaccinations and autism, Dr Zerbo stressed that "we know through numerous scientific studies that there is no association between childhood vaccination and the incidence of autism spectrum disorders".
Nevertheless, Dr Zerbo said his team found "large disparities in vaccination rates between children with and without autism spectrum disorders, as well as between their siblings".
Partaking in the study were over 590 000 children born in California, Colorado, Oregon and Washington state between 1995 and 2010 who did not have autism, alongside more than 3 700 children who did.
Investigators tracked vaccination histories among all of the children through 2015. Vaccination records among younger siblings (born between 1997 and 2014) were also reviewed.
Family vaccination records were then stacked up against immunisation recommendations for kids between the 1 month and 12 years old.
Among children aged four to six, the team found that children with autism were "significantly less likely" to receive the full range of recommended vaccines, compared with other children.
Vaccination rates among siblings of children with autism were also "significantly lower" across all age groups.
Compared with parents of children without autism, parents of children with autism were found to be more likely, overall, to decline at least one vaccination for a younger healthy sibling, and more likely to fail to fully vaccinate younger offspring before they reached one year old.
Figures for immunisation coverage in South Africa may be unreliable due to the lack of standardised user-friendly data collection tools nationally.
Given the large number of participants, Dr Zerbo said the findings are likely generalisable to all Americans, despite having focused on the West and Pacific Northwest regions.
The findings were published online in the journal JAMA Pediatrics.
"Our next steps in this research will be to better understand why parents of children with autism may be hesitant to vaccinate them and their siblings," Dr Zerbo said.
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