The publication of the paper by Ousseny Zerbo and colleagues  garnered some media headlines insofar as their conclusion that: "Children with ASD [autism spectrum disorder] and their younger siblings were undervaccinated compared with the general population."
Drawing on data from "6 integrated health care delivery systems across the United States within the Vaccine Safety Datalink" researchers looked at immunisation status for over 3700 children diagnosed with ASD and over half a million kids not diagnosed with autism alongside their respective younger siblings. They were specifically looking at the proportion of children who "received all of their vaccine doses according to ACIP [Advisory Committee on Immunization Practices] recommendations."
Results: "For vaccines recommended between ages 4 and 6 years, children with ASD were significantly less likely to be fully vaccinated compared with children without ASD." Vaccination rates were also significantly lower for younger siblings of those with autism too. Further discussion of the details of the Zerbo results can be seen here.
Although headline grabbing, this research topic - vaccination rates among children with autism and their siblings - is by no means a new one (see here and see here for examples). The Gena Glickman findings  published last year (2017) for example, did not attract the same degree of media attention but highlighted how (a) parents of children diagnosed with autism were extremely vaccine compliant when it came to their earlier born children, and (b) "Families with children who had autism spectrum disorder were less likely to vaccinate subsequent children." To quote from some of the media on the latest Zerbo paper: ""We did not look at vaccination rates before the children were diagnosed with autism," Zerbo noted"; a pretty important omission by all accounts.
What's then also missing from the current data in this area? Well, the question of why - why are children with autism and their siblings less likely to be vaccinated - is a rather glaring omission, and one that stretches into other age ranges  too. Yes, it's easy to say that 'fear of the autism-vaccine link' is a primary reason for the undervaccination statistics, particularly with the data on age being a factor in the Zerbo findings and despite the 'too many too soon' argument having some strong evidence against it (see here). But... as per the Glickman and other data, many parents are/were extremely vaccine compliant when it came to earlier born children. If they were going to have long-standing fears about vaccination and indeed, act upon those fears, I would have thought that they would have influenced vaccination behaviour across all their children and not just as and when autism was diagnosed in a family member. Neither do I give much [research-based] credence to the idea that parents of children with autism are somehow over-represented among the so-called 'anti-vaxxer' groups (see here); not that is, as being a long-standing issue.
Glickman et al do provide another possible explanation in their study results that: "changes in vaccination behavior may relate to adverse reactions to vaccine" in their cohort. A sort of once bitten, twice shy sentiment if you like *might* potentially be in action, which kinda makes more sense. I know this takes us down a rather uncomfortable path in that, whilst acknowledging that vaccines represent an important cornerstone of modern healthcare (yes, they do), they are not somehow magically without side-effects for some. Hackles are bound to be raised by such utterances; despite some potentially important clues already appearing in the peer-reviewed research literature  relevant to this topic. But without even attempting to try and answer such 'why' questions, we are left with a fairly large number of children who "are at increased risk of vaccine-preventable diseases" with no real solutions in sight for protecting their health and/or the health of the wider population.
Answers are therefore required and required quickly. The simplest and perhaps most logical solution I can see would be to go and ask parents/primary caregivers, under scientifically controlled study, why their children are undervaccinated; perhaps building on important work such as that by Hilton and colleagues . There is the issue of recall to overcome (see here) and I'm sure the range of answers is going to be long and complicated in relation to undervaccination. Armed however, with such answers or at least clues from the parents/caregivers themselves and not just 'speculation', science and policy can perhaps then start to move things forward to further protect the health of all concerned. Hopefully also, such knowledge can be used to chip away at yet another important health inequality that seems to follow a diagnosis of autism throughout the lifespan (see here)...
 Zerbo O. et al. Vaccination Patterns in Children After Autism Spectrum Disorder Diagnosis and in Their Younger Siblings. JAMA Pediatrics. 2018. Mar 26.
 Glickman G. et al. Vaccination Rates among Younger Siblings of Children with Autism. N Engl J Med. 2017 Sep 14;377(11):1099-1101.
 Filliter JH. et al. The next vaccine-autism question: Are school-aged youth with autism spectrum disorder undervaccinated and, if so, why? Paediatr Child Health. 2017 Aug;22(5):285-287.
 Poling JS. et al. Developmental regression and mitochondrial dysfunction in a child with autism. J Child Neurol. 2006 Feb;21(2):170-2.
 Hilton S. et al. MMR: marginalised, misrepresented and rejected? Autism: a focus group study. Archives of Disease in Childhood. 2007;92(4):322-327.