When you see the phrase “monkey business” in a headline about autism research,
you’re not wrong to suspect that something has gone scientifically sideways.
In this case, the mischief isn’t coming from the monkeys it’s coming from
how their data are used (and abused) to prop up a tired, evidence-free claim:
that vaccines cause autism.
In the late 2000s, a small, deeply flawed primate study was promoted as
“proof” that the hepatitis B vaccine and the mercury-containing preservative
thimerosal could damage newborn brains and somehow lead to autism. It was
loudly celebrated by anti-vaccine activists and just as loudly criticized by
scientists who actually read the methods section. This article revisits that
“monkey business,” updates the story with what we’ve learned since, and
explains why the science-based conclusion hasn’t changed: vaccines do not
cause autism, and bad research doesn’t become good just because it involves
adorable primates and dramatic press releases.
How we got here: From thimerosal scares to hepatitis B panic
To understand why anyone would run an autism-related study in baby monkeys
in the first place, you have to rewind to the late 1990s and early 2000s.
This was the era of the infamous, now-retracted paper by Andrew Wakefield
that claimed a link between the MMR (measles, mumps, rubella) vaccine and
autism. That paper was later exposed as methodologically unsound and riddled
with undisclosed financial conflicts and likely fraud, but the damage to
public trust lingered.
As larger, better-designed studies repeatedly failed to find any link
between MMR and autism, the hypothesis shape-shifted. Attention turned to
thimerosal, a mercury-containing preservative that had been used in some
childhood vaccines. The fear was simple but misleading: “Mercury is bad,
thimerosal is mercury, therefore thimerosal must be causing autism.” Never
mind that thimerosal contains ethylmercury (which is processed and
cleared from the body differently than the methylmercury found in
contaminated fish), or that the actual exposure levels from vaccines were
tiny.
Public health agencies in the United States eventually removed thimerosal
from routine childhood vaccines (with the partial exception of some flu
shots) as a precautionary move. But here’s the key point: while thimerosal
was being phased out, researchers were already looking very closely for any
link to autism. Multiple large epidemiologic studies and the 2004
Immunization Safety Review by the National Academies concluded that the
evidence favored rejecting a causal relationship between
thimerosal-containing vaccines and autism. The same committee came to the
same conclusion about MMR and autism. The scientific consensus was clear
long before the preservative disappeared from most vaccines.
Once the “thimerosal did it” idea collapsed under data, anti-vaccine
activists did what they always do: they looked for a new villain. Hepatitis
B vaccine, given shortly after birth, was a perfect candidate. It happens
early, it sounds scary, and it’s easy to spin misleading stories like “Why
are we giving a sexually transmitted disease vaccine to newborns?” while
conveniently ignoring other routes of transmission (like contaminated blood
or an infected parent) and the very real dangers of chronic hepatitis B
infection.
The infamous monkey study: What actually happened?
Enter the monkey study. A team including Andrew Wakefield and Laura Hewitson
performed a small experiment in infant rhesus macaques. Their paper, with a
very dramatic title about “delayed acquisition of neonatal reflexes,” was
promoted heavily by anti-vaccine groups as proof that a
thimerosal-containing hepatitis B (HB) vaccine could cause neurological
harm.
On paper, the design sounds impressive: a “prospective, controlled,
observer-blinded” study of neonatal reflexes in baby macaques given a
hepatitis B vaccine within 24 hours of birth. In practice, there were enough
methodological red flags to decorate a very skeptical Christmas tree.
Problem #1: Tiny sample sizes and lopsided groups
One of the first things you learn in clinical research is that very small,
unbalanced groups are a recipe for unreliable results. In earlier abstract
versions and related work, the “vaccinated” group contained several times
more monkeys than the control group (think 13 versus 3), which is nowhere
near adequate for robust statistical power. Even in the published version,
the overall numbers were small.
When you’re working with such tiny samples, any apparent difference between
groups can easily be noise: a random fluctuation dressed up as a meaningful
signal. This is especially true when measuring something as variable as
behavior or reflexes in newborn animals. If you toss a coin three times and
get two heads and one tail, you don’t conclude that the coin is unfair. But
that’s roughly the level of over-interpretation we’re dealing with here.
Problem #2: A model in search of a disease
At the heart of the study is a conceptual problem: there is no widely
accepted primate model of autism. Autism spectrum disorder (ASD) is a
complex neurodevelopmental condition, defined in humans by differences in
communication, social interaction, and behavior over years of development.
You cannot meaningfully diagnose “autism” in a few weeks of observing baby
monkeys.
To fill this gap, the researchers focused on primitive neonatal reflexes,
such as the rooting or sucking reflex. But it’s far from clear how minor
timing differences in these reflexes in macaques map onto autism in humans,
if they do at all. Primitive reflexes in human babies are usually present at
birth and fade over time, and variations can be influenced by many factors:
birth weight, gestational age, anesthesia during delivery, and even how
carefully you measure them.
In other words, the study’s core assumption that tiny shifts in neonatal
reflexes in vaccinated monkeys somehow illuminate the origins of human
autism is speculative at best. It’s like trying to infer the health of
your car’s engine by tapping the horn once and listening very carefully.
Problem #3: Artificially re-creating the “old” vaccine
By the time this paper was published, the real-world hepatitis B vaccines
used for infants in the United States no longer contained thimerosal.
So what did the researchers do? They added thimerosal back into the vaccine
used in the study to mimic the 1990s formulation.
That means the experiment doesn’t reflect the vaccine schedule that actual
children were receiving in the late 2000s, let alone today. Even the authors
admitted that the design couldn’t distinguish whether any observed effect
was due to the vaccine itself, the thimerosal, or both. If your goal is to
understand the real-world risk of current vaccines, creating a
“Franken-vaccine” that no longer exists is a strange place to start.
Problem #4: Conflicts of interest that would make anyone blush
The conflicts of interest in this study were not subtle. Key authors had
served as paid expert witnesses in vaccine litigation and had children
involved in the National Vaccine Injury Compensation Program. The work
received support from organizations whose entire mission is to prove that
vaccines cause autism.
None of that automatically makes the data wrong but it does raise serious
questions about how hypotheses are framed, how analyses are chosen, and how
results are interpreted and publicized. The irony is that some of the same
activists who denounced mainstream vaccine researchers for any connection to
public health agencies or manufacturers suddenly discovered that conflicts
of interest don’t matter when the conflicts are on their side.
What real vaccine–autism research looks like
So what does solid, science-based autism research look like? Hint: it doesn’t
hinge on a dozen monkeys and some hand-wavy behavior scoring.
Over the last two decades, multiple lines of evidence have converged on the
same conclusion:
-
Large epidemiologic studies in the United States and other
countries have compared hundreds of thousands of vaccinated and
unvaccinated children and found no difference in autism rates attributable
to MMR, hepatitis B, or thimerosal-containing vaccines. -
Independent reviews by expert panels, including the
Institute of Medicine (now the National Academy of Medicine), have
repeatedly examined all available data and concluded that the evidence
favors rejecting a causal link between vaccines and autism. -
Mechanistic research exploring how autism develops points
to complex genetic and early developmental factors, not a single
environmental trigger like a vaccine shot. -
Real-world experience since thimerosal was removed from
most childhood vaccines shows no decline in autism diagnoses. If
thimerosal were a major driver of autism, you’d expect rates to drop after
exposure decreased. They didn’t.
You don’t need to take the word of any single scientist or organization. The
power here comes from converging evidence, from multiple teams, across
different countries and methodologies. That’s what “science-based” actually
means: not one dramatic primate study, but a consistent story across many
good studies.
2025 déjà vu: When politics tries to rewrite the science
Fast-forward to today, and you might feel like we’re living in a time loop.
Recent political interference in how government agencies talk about vaccines
and autism has stirred confusion. Changes to official websites and memos
that overemphasize tiny, uncertain risks while downplaying clear benefits
can make it seem as if the science has suddenly changed.
It hasn’t.
The underlying evidence that vaccines do not cause autism remains robust.
What’s shifting is not the data but the messaging sometimes driven by
political appointees with long-standing anti-vaccine leanings. That’s why
organizations of pediatricians, epidemiologists, and infectious disease
experts have pushed back, emphasizing that well-controlled studies still
show no causal link between childhood vaccines and autism.
The lesson is the same one we learned from the monkey business of 15+ years
ago: bad research, misinterpreted data, or politically skewed communication
can cause enormous harm if the public doesn’t have the tools to spot the
problems. Which brings us to those tools.
How to spot “monkey business” in autism research
When you encounter a new claim about vaccines and autism especially one
that seems to overturn decades of research overnight it helps to run
through a quick checklist:
-
Sample size and design: Are we talking about hundreds of
thousands of children or a dozen monkeys? Was the study randomized,
blinded, and adequately powered? -
Relevance of the model: If animal models are used, do
they actually mimic key features of autism, or are the researchers
stretching weak behavioral endpoints to fit a preconceived story? -
Consistency with other data: Does this result align with
or contradict many other high-quality studies? One small outlier study
doesn’t overturn a mountain of evidence. -
Conflicts of interest: Who funded the work? Are the
authors involved in litigation or advocacy groups that have already picked
a side? -
Media amplification: Is the study being loudly promoted
by advocacy sites and social media before it has been fully peer-reviewed
or contextualized?
If the answers look a lot like the old monkey study tiny sample sizes,
speculative models, heavy activist promotion, and glaring conflicts of
interest you can safely file it under “monkey business” rather than
“medical breakthrough.”
Respecting autistic people while rejecting bad science
There’s another reason why vaccine–autism myths are so harmful: they
stigmatize both vaccines and autistic people. Framing autism as a tragedy
caused by something “done” to a child invites guilt, blame, and the pursuit
of questionable “cures.” It also distracts from the real work of supporting
autistic individuals and their families with appropriate services,
accommodations, and respect.
Science-based medicine doesn’t just protect vaccines; it protects people.
Good research on autism focuses on early identification, effective supports,
and understanding the full range of neurodiversity not on hunting down a
vaccine scapegoat that simply isn’t there.
Stories from the front lines: Experiences with vaccine myths and “monkey business”
It’s one thing to argue about p-values and primate models. It’s another to
see how vaccine–autism myths and questionable studies affect real people in
exam rooms, classrooms, and communities. To bring this home, let’s look at
a few composite experiences inspired by what clinicians, researchers, and
families have reported over the years.
In the pediatrician’s office
A young couple, new parents, sit in a pediatrician’s office with their
2-day-old baby. The appointment is supposed to be routine weight check,
feeding support, first hepatitis B shot. But Mom pulls out a printout from a
website, complete with screenshots of baby monkeys and alarming captions
about “brain damage from newborn vaccines.”
The pediatrician has seen this before. Instead of rolling their eyes, they
sit down and walk through the facts: what hepatitis B is, how it can be
transmitted, why universal newborn vaccination protects not just their baby
but the healthcare system as a whole. They explain that the monkey study was
tiny, methodologically weak, and out of step with large human studies that
show no autism link. They also acknowledge something important: “You’re not
wrong to be scared. You’re being bombarded with scary stories. My job is to
help you sort stories from science.”
Sometimes that conversation works right away. Sometimes it takes a few
visits. But it always starts with respect and with the confidence that
comes from knowing the evidence, not just the headlines.
At a research conference
Imagine being a neurologist or epidemiologist attending a scientific
meeting. You’ve spent your career studying autism: genetics, early brain
development, environmental factors that actually show up in data. Then you
see a poster or talk being hyped on social media as the “study that finally
proves vaccines cause autism.”
You walk over. The sample size is tiny. The outcome measures are fuzzy. The
statistical analysis is… generous. You ask a few questions, and it quickly
becomes clear that the authors started with a conclusion (“vaccines cause
harm”) and worked backward.
Researchers have described this feeling as equal parts frustration and
determination. Frustration, because they know how eagerly such work will be
amplified by anti-vaccine activists; determination, because it underscores
the need to communicate good science clearly to the public. The “monkey
business” isn’t just annoying it actively competes with solid research for
attention, funding, and trust.
For families in the autism community
Many parents of autistic children describe a familiar arc. At first, they’re
desperate for answers. Someone sends them a link about vaccines and autism,
maybe featuring that same primate study or others like it. The story is
simple and emotionally powerful: “This shot did this to your child.”
Over time, as they meet autistic adults, therapists, and clinicians who
understand the actual science, many realize that the vaccine narrative
doesn’t hold up and that clinging to it may be preventing them from fully
seeing their child as they are, not as a “before and after” tragedy.
Several autism advocacy organizations led by autistic people and
science-minded parents have been vocal about this. They argue that blaming
vaccines not only undermines public health but also fuels stigma and
distracts from real needs: inclusive education, accessible healthcare,
employment supports, and societal acceptance.
Why these experiences matter
These human stories are why the details of primate studies, statistical
power, and conflict-of-interest disclosures are not just academic hairsplitting.
When flawed research is used to scare parents out of vaccinating, outbreaks
of preventable diseases follow. When autism is framed as a vaccine injury
instead of a neurodevelopmental difference, autistic people are treated as
broken rather than supported.
“Monkey business in autism research” isn’t just a clever title. It’s a
reminder that we have to be vigilant as clinicians, researchers, and
citizens about how science is done, interpreted, and communicated. The
goal isn’t to win an argument on social media. It’s to protect children from
both preventable infections and preventable misinformation, while respecting
and supporting autistic people as full members of our communities.
Conclusion: Don’t confuse noise with signal
In the end, the story of the monkey study and its modern echoes is a
textbook example of how not to do, or use, autism research. A small, noisy,
methodologically shaky experiment was elevated to the status of a
world-shaking discovery, largely because it fit a pre-existing narrative
cherished by the anti-vaccine movement.
Science-based medicine asks a different question: What does the totality of
high-quality evidence show? When you look at large human studies, careful
reviews by independent expert panels, and decades of experience with
vaccines, the answer is consistent: vaccines do not cause autism. The
hepatitis B vaccine protects infants from a serious viral infection; it
doesn’t rewire their brains into autism. Thimerosal, at the levels used in
vaccines, has not been shown to cause autism. Removing it didn’t change
autism rates.
That doesn’t mean vaccines are risk-free no medical intervention is. It
means we should evaluate those risks honestly, based on solid evidence, and
compare them to the very real risks of the diseases vaccines prevent. When
studies in monkeys or humans are well-designed, adequately powered, and
transparently analyzed, they should be welcomed and scrutinized. When
they’re not, we should be just as ready to call them what they are:
monkey business.
