Kids diagnosed with autism are less likely than the general population to receive the recommended set of safe and protective vaccines—and so are their younger siblings, according to a new observational study in JAMA Pediatrics.

The finding indicates that children with autism and their siblings are at an increased risk of contracting preventable—and dangerous—infectious diseases. It also suggests that a pernicious and completely bogus notion that vaccines cause autism may be spurring hesitancy in some parents.

The authors of the study note in their conclusion:

Previous studies reported that a large proportion of parents of children with ASD [autism spectrum disorder] 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.

The study was conducted by a nationwide group of health researchers from Kaiser Permanente and the Centers for Disease Control and Prevention. Together, they looked at medical records of a racially/ethnically and socioeconomically diverse population of nearly 600,000 children from six locations around the country.

Methodology

This included 3,729 kids diagnosed with autism, all born between January 1995 and September 2010. The researchers determined an autism diagnosis based on the presence of medical codes for an autism diagnosis appearing in a child’s health records on at least two separate occasions. Previous research had found this method was valid for identifying autism cases.

The researchers compared their vaccine rates to children without an autism diagnosis, matched by age, sex, and location. They then looked at the younger siblings of children with autism, born between January 1997 and September 2014. Those siblings were also compared with matched children, who were younger siblings of kids without an autism diagnosis.

For the analysis, researchers started with the recommended vaccination schedule for kids aged four to six, which includes the MMR vaccination (Measles, Mumps, and Rubella) that has been most often (falsely) alleged to cause autism. Only 81.6 percent of 2,855 kids with autism in that age bracket were fully vaccinated with this batch of vaccines, compared with 94.1 percent of 483,961 kids in that age bracket without autism.

Next, the researchers looked at the recommended batch of vaccines for kids 11 to 12 years old. This included the HPV vaccine and Tdap (Tetanus, diphtheria, and pertussis) vaccine. The researchers didn’t see a difference here. Of 874 children in this age bracket with autism, 77.5 percent were fully vaccinated compared with 76.9 percent children without autism.

Together, the results suggest that some parents may see the vaccines recommended at a younger age as riskier than vaccines given later. This played out in the sibling analysis, too.

Younger siblings of kids with autism were less likely to get vaccines across the board—regardless of which batch of vaccines the researchers assessed. For instance, only 73 percent of 881 siblings of kids with autism were fully vaccinated with the batch of vaccines given between one and 11 months. On the other hand, out of 189,144 younger siblings of kids without autism, 85 percent were fully vaccinated. But the difference broke down in the older vaccination schedule, with siblings of kids with autism only slightly behind their counterparts (63 percent vs 65 percent).

While the study may not catch all cases of vaccine hesitancy and refusal, the researchers say it’s enough to call for a change. They suggest new strategies, such as those promoting more dialogue between parents and doctors, to help dispel vaccine myths and protect children.

JAMA Pediatrics, 2018. DOI: 10.1001/jamapediatrics.2018.0082 (About DOIs).