March 26 (UPI) -- Children with autism and their younger siblings were less likely to be fully vaccinated compared with the general population even though scientific studies have shown no link, according to a study by Kaiser Permanente.
Researchers examined health records and immunization data on nearly 500,000 children from a database collected by the Centers for Disease Control and Prevention at six sites, publishing their findings on Monday in the Journal of American Medicine's Pediatrics.
An estimated 1 in 68 school-aged children have been identified with autism spectrum disorder, according to the CDC.
"In this large and comprehensive study, we found that after children received an autism diagnosis, the rates of vaccination were significantly lower when compared with children of the same age who did not have an autism diagnosis,"Dr. Ousseny Zerbo, a postdoctoral fellow with the Kaiser Permanente Northern California Division of Research, said in a press release.
Researchers analyzed data on the vaccination of 3,729 children at least 7 years old with autism spectrum disorders who were diagnosed by 5 years of age, 483,961 children without ASD that were born between Jan. 1, 1995 and Sept. 30, 2010, and their younger siblings that were born between Jan. 1, 1997 and Sept. 30, 2014.
"There were large disparities in vaccination rates between children with and without autism spectrum disorders, as well as between their siblings, across all age groups and after adjusting for important confounding factors," senior author Dr. Nicola Klein, director of the Kaiser Permanente Vaccine Study Center said.
Among children aged 7 years or older, 94 percent of those without autism received all vaccines recommended between 4 and 6, compared with 82 percent of those with an autism
For the measles, mumps, rubella, or MMR vaccine, the rates were 96 percent of those without autism and 84 percent of those with it.
For the siblings of children who have autism, the rates were event less -- 73 percent of younger siblings of children with autism were fully vaccinated, compared to 85 percent of younger siblings of children without autism.
"Numerous scientific studies have reported no association between childhood vaccination and the incidence of autism spectrum disorders," said Dr. Frank DeStefano, a researcher with the CDC's Immunization Safety Office. "Nonetheless, this new study suggests that many children with autism and their younger siblings are not being fully vaccinated.
The study was not designed to address why vaccination rates were lower among children with autism and their siblings, but researchers speculated the lower numbers are linked to parental concerns.
"Although we do not know all factors contributing to undervaccination among children with ASD, the results of our study suggest that parental vaccine refusal could have a role," researchers wrote in the study. "Previous studies reported that a large proportion of parents of children with ASD consider that vaccines contributed to their child's ASD, and consequently they either changed or discontinued vaccination, suggesting that current strategies to address vaccine hesitancy have not been effective for parents of children with ASD. New strategies, including establishing or promoting a better dialogue among parents, health care professionals, and public health authorities, may be needed to increase vaccine uptake in populations with low uptake."
Robin P. Goin-Kochel, an associate director for research at the Autism Center of Texas Children's Hospital in Houston who was not involved in the study, pointed out to CNN that the focus of the study "largely on Western/Pacific states" and the attitude toward vaccination in these places may be "more representative of families in this particular part of the country."