This answer briefly summarizes some overarching inferences,
- / (Autism Spectrum Disorders, ASD) rates started greatly increasing in some countries such as the US and UK since the 1980s even as doctors little understood these conditions and offered little of value to increasingly anxious parents desperately seeking definitive answers. Thus, in such an Autism causation vacuum, et al’s 1998 Lancet report ( ), the first to offer an explanation for the ‘autism epidemic’, became a convenient crutch for many frustrated parents who felt either ignored or condescended to by the medical establishment.
- However, in ~20 years, there’s surprisingly scant scientific evidence to support the contention that ‘vaccines cause autism’. Surprising because 20 years is a long enough period to be able to bolster the argument with solid data sets.
- Even taken at face value, many risk factors about Autism/ASD simply cannot be explained by a ‘vaccines cause autism’ notion. The more facts it can explain about a given phenomenon, the stronger a given hypothesis. That is just not the case with the ‘vaccines cause autism’ notion, which is simply inherently scientifically weak.
On a topic so controversial as a potential vaccine(s)-Autism link, it may be best to start by scrutinizing the original data that got this particular idea started. In 1998, Andrew Wakefield and 12 co-authors published a Lancet article on 12 children, claiming they had identified in them evidence of a novel syndrome they called( ).
To digress just a bit at first, it’s somewhat surprising that there isn’t yet an agreed-upon consensus on the etiquette regarding scientific papers that have been retracted (2,). Specifically, should they continue to be cited in the literature or not? For example, this Wakefield et al paper continues being cited, 85 times already over six months in 2017 according to Google Scholar.
This answer however requires not just citing this paper but also looking at what it actually says since it subsequently served as the launchpad for a purported vaccine(s)-Autism link. While 8 of these 12 children (67%) had received the MMR vaccine by the time of their symptom onset, the authors concluded (see below from, emphasis mine),
‘We identify associated gastrointestinal disease and developmental regression in a group of previously normal children, which was generally associated in time with possible environmental triggers…We did not prove an association between measles, mumps, and rubella vaccine and the syndrome described…If there is a causal link between measles, mumps, and rubella vaccine and this syndrome, a rising incidence might be anticipated after the introduction of this vaccine in the UK in 1988. Published evidence is inadequate to show whether there is a change in incidence22 or a link with measles, mumps, and rubella vaccine.23′
Since these authors did suggest ‘a rising incidence [of their newly coined syndrome] might be anticipated after the introduction of this [MMR] vaccine in the UK in 1988‘, if we give them the benefit of the doubt and assume their autistic enterocolitis concords to some extent with Autism, what do epidemiological data show so far? In a nutshell, nothing that supports their supposition. On the contrary, such studies haven’t found a link between vaccines and Autism.
- A 1999 study of children in North Thames, London, found rising cases of ASD since 1979 without a sharp increase after MMR was introduced in 1988 ( ).
- A 2001 British study found that while Autism rates in 2 to 5 year olds had increased from 8 boys per 10000 to 29, a 3.6-fold increase, from 1988 to 1993, rates of MMR vaccination had remained stable across these birth cohorts, meaning it wasn’t possible to attribute the Autism rate increase to the MMR vaccine ( ).
Thus an examination of the original paper that jump-started the vaccines-Autism controversy finds it did not even make such an assertion and that subsequent studies found no evidence of such a link either. OTOH, one detailed review after another has since found that the MMR vaccine
- Is safe ( , ).
- Is unlinked to Autism ( ).
The furore, notoriety and controversy about a link between vaccines and Autism begins with this one study of a mere 12 children, only 8 of whom had received the MMR vaccine by the time of their symptom onset, and it turns out the study didn’t even make that claim. Also more accurately, the paper explores not a link between vaccines and Autism in general but rather one specifically between the MMR vaccine and autistic enterocolitis, a syndrome that isn’t listed in medical textbooks.
So, how did a link between vaccines and Autism even get made? Turns out to have been a subsequent interpretation (), perhaps helped along by an immediate press conference when this paper was published followed by copious contemporaneous sensationalist front-page coverage by several British newspapers ( ) of a kind that suggests ( ) many couldn’t even be bothered to read what was actually in the paper.
Subsequent uncovering of undisclosed conflicts of interest behind Wakefield’s study followed by predictable establishment backlash against him then cast him in the potent ‘martyr’ mode, which further solidified and enhanced his reputation among parents desperately seeking definitive answers to their children’s Autism/ASD diagnosis, and who also felt Wakefield took them seriously while feeling the medical establishment didn’t ().
How Autism’s Causation Vacuum was Fertile Soil for Wakefield’s Vaccine-Autism Supposition to take Root
On the face of it, it seems astounding that one small study on 12 patients should have had such an outsize impact. And yet, maybe not so surprising from a sociological perspective. At the time the Wakefield et al paper came out, Autism/ASD rates had already been spiking for several years with no satisfactory explanation from the medical establishment. Perhaps unwittingly, this state of affairs helped stoke and sustain this particular controversy.
- Autism diagnosis remains the purview of behavioral scientists who base the diagnosis on a highly subjective checklist, not an impartial, objective, quantitative diagnostic test.
- Even as they tweaked and improved their diagnostic toolkit, which in turn led to increasing rates of diagnosis, doctors had no clear answer for why steadily increasing numbers of children were being diagnosed with Autism from the 1980s, especially in the US and UK.
- Still little understood, neither reliable objective diagnosis nor specific treatment, let alone cure, yet existed for Autism/ASD, a situation little changed in the years since.
- With increasing numbers of parents desperately seeking answers to their children’s predicament, a causation vacuum concerning Autism was precisely calamitous and in hindsight, the Wakefield paper appears to have arrived at just the right moment to fill it with something that no one had proposed thus far, a ‘medical explanation for the autism epidemic‘ (see below from , emphasis mine).
‘However, the fact that there was no other reported or known reason for the ‘epidemic’ did not exactly help matters. Whatever their overall validity, vaccine hypotheses did plug a gaping hole in scientific knowledge about this condition that everyone thought had been measured so precisely and accurately with a wealth of new measurement tools and scales. How could it be that no one actually knew why autism was increasing?…Wakefield’s work was so popular because it promised so much. It promised to fully explain the autism epidemic, thus it was particularly ironic that epidemiological sciences never supported his claims.’
- Autism/ASD having historically been and tending to remain the purview of behavioral scientists may, in the grand scheme of things, turn out to have been a major stumbling block that stymied accelerated understanding of these conditions.
- Ironically, by highlighting gastrointestinal issues in autistic children, Wakefield may have done Autism/ASD research a huge service. After all, ~20 years on, the gut microbiota-brain link is so much better appreciated now and indeed gut is today well-recognized as a cardinal feature in substantial numbers of Autism/ASD patients (10, ).
- There was and is an urgent need for a more multi-disciplinary approach for both research and diagnosis in the Autism/ASD field. Gastroenterologists, immunologists, microbiologists, geneticists and other specialists would only help not impede better understanding of these conditions by helping develop more scientifically robust diagnostic approaches and helping tailor more targeted therapies.
- Even in 2017, such cross-disciplinary research on Autism/ASD is sorely lacking. A simple literature search is a clear indication of this. My search for ‘Autism’ in both Nature Reviews Immunology and Nature Reviews Microbiology together turned up a total of only 24 articles, 2001-2017 ( ), only 19 in Nature Reviews Gastroenterology and Hepatology, though through 2006-2017, which suggests the gut-microbiota-brain axis is becoming a bigger focus of research ( ), while the same search in Nature Reviews Neuroscience turned up almost 10X higher articles (219), 2001-2017 ( ). For context, the Nature Reviews series are typically considered among the most influential science review journals for various subjects.
- History also suggests the Wakefield idea fills the Autism/ASD causation vacuum rather like a square peg in a round hole. After all, it is inherently scientifically weak since there are so many Autism/ASD risk factors that effects of vaccines, adverse or otherwise, simply cannot explain.
So many Autism/ASD Risk Factors that Vaccines can’t explain
How could vaccines possibly explain
- Why Autism/ASD is more common in boys than girls, ranging from ~4:1 in the 1990s ( ) to ~9:1 by the 2010s ( , , )? If vaccines ’cause’ autism, a person’s gender shouldn’t matter.
- Why Autism/ASD rates are so much higher in monozygotic (identical) (70-90% concordance) compared to dizygotic (fraternal) (0-30% concordance) twins (
, , )?
- Found in disparate populations such as in the UK ( ) as well as in Scandinavia (23).
- Monozygotic twin concordance for autism is a long-standing feature, being observed right from the 1970s in pioneering studies by (24).
- Autism thus has an unmistakably strong genetic component ( ), something that could not be explained by environmental factors alone such as effects of vaccine(s), adverse or otherwise.
- If vaccines ’cause’ autism, a person’s genetic background shouldn’t matter.
- Autism/ASD connection with maternal and child antibiotic use reported in several studies (25, 26, 27)? This alludes to a different environmental trigger, namely, changes in gut microbiota composition.
- Consistently identified Autism risk factors such as exposure to traffic-related air pollutants, increased parental age, maternal obesity, diabetes and folic acid deficiency, prenatal viral infection, C-section, preterm birth, low birth weight, limited or absent breastfeeding, abnormal melatonin synthesis, hyperbilirubinemia, zinc deficiency, and maternal immigrant status ( , , , , , )? These factors and vaccines are simply unconnected.
Autism/ASD are clearly multi-factorial, with both genetic and environmental factors intersecting in as-yet undeciphered ways, and since rates started to increase dramatically since the 1980s, clearly some environmental factor(s) are key. However, those factors still remain stubbornly unclear. Rather than vaccines, however, multiple studies since at least 2004 have consistently reported altered gut microbiota composition in ASD subjects (10,). Whether that’s cause or effect still remains to be determined.
Basing anti-vaccine sentiment on a purported vaccines-autism link is reckless and dangerous since it inflicts real cost in the form of needless deaths from vaccine preventable diseases. Consider measles where the vaccine is historically one of the safest on record. In June 2017, a six year old Italian leukemia patient died from measles complications after reportedly catching it from his older brother, whom his parents had decided not to vaccinate (), the latest in a measles ‘tragedy’ that has so far taken 35 lives across Europe ( ).
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