New Study on Vaccines and Neurodevelopment

This week, I want to discuss a study (using this term loosely) that has sparked debate over a supposed link between vaccinations and neurodevelopmental disorders (NDDs), including autism spectrum disorder (ASD). At first glance, the study’s findings may seem alarming, but a closer look reveals serious flaws in methodology, biases, and misinterpretations that render its conclusions unreliable.

Fair warning: This week’s newsletter is longer than usual and dives deeply into a topic that has sparked significant discussion. Given the scope and implications of the study in question, I felt it was necessary to thoroughly address its claims, flaws, and the broader context. Let’s break it down together, step by step, to ensure you have the full picture.

Key Findings and What They Claim

• Study Design: This was an observational study based on Florida Medicaid billing claims data.

• Population: The study analyzed 47,155 children enrolled in Florida Medicaid from birth to age 9.

• Group Comparison: Children were categorized as "vaccinated" (based on the presence of vaccine billing codes) and "unvaccinated" (absence of such codes).

• Data Sources: Both vaccination status and NDD diagnoses were determined using billing codes.

The study presented the following findings:

• Association Between Vaccination and NDDs: Vaccinated children were reported to have significantly higher odds of being diagnosed with NDDs compared to unvaccinated children.

• Impact of Preterm Birth: Preterm children who were vaccinated had a higher prevalence of NDDs (39.9%) compared to unvaccinated preterm children (15.7%), with an odds ratio of 3.58 (95% CI: 2.80, 4.57).

• Dose-Response Relationship: The researchers claimed that the risk of ASD increased with the number of vaccination visits.

  • Children with one vaccination visit were 1.7 times more likely to be diagnosed with ASD compared to unvaccinated children (95% CI: 1.21, 2.35).

  • Children with 11 or more vaccination visits were 4.4 times more likely to be diagnosed with ASD compared to unvaccinated children (95% CI: 2.85, 6.84).

These claims may seem striking, but they fail to account for critical factors that explain these observations without implicating vaccines.

The Origins of the Research: A Questionable Foundation

The study was published in Science, Public Health Policy and the Law, a journal not widely recognized within the scientific community. Its reputation is questionable, with unclear peer-review standards and a history of publishing articles that align with anti-vaccine rhetoric.

Lack of Adequate Peer Review:
Credible scientific research relies on rigorous peer-review processes, ensuring findings are critically evaluated by independent experts before publication. Unfortunately, the journal in question does not meet the high standards of established, reputable publications in public health or medicine.

The Lead Author’s Troubling History:
The lead author, Anthony Mawson, has a documented history of conducting methodologically flawed vaccine research. Several of his previous studies have been retracted due to ethical violations and lack of scientific rigor. This alone raises red flags about the reliability of this study.

Anti-Vaccine Funding and Propaganda:
The study was funded by the National Vaccine Information Center (NVIC), a known anti-vaccine advocacy organization. This funding source introduces significant bias and compromises the study’s credibility. The fact that this study aligns so conveniently with anti-vaccine talking points deepens skepticism.

Promoted via Blogs, Not Science Channels:
Adding to the concern, the study was prominently shared on a WordPress blog rather than through traditional academic or scientific outlets. This is a common tactic in anti-vaccine propaganda: bypassing rigorous academic scrutiny, appear official, spread their misinformation and instead disseminating misleading findings directly to the public.

Dr. Peter A. McCullough’s Role:
The study was "peer-reviewed" by Peter McCullough, a known promoter of medical misinformation. This bypassed legitimate scientific scrutiny, as McCullough has a history of spreading unfounded claims about vaccines, further eroding the study’s credibility.

Misinterpreting Healthcare Utilization: A Critical Flaw

One of the study’s key claims is that the number of vaccination visits correlates with an increased risk of ASD. Specifically:

• Children with one vaccination visit were 1.7 times more likely to be diagnosed with ASD (95% CI: 1.21, 2.35).

• Children with 11 or more vaccination visits were 4.4 times more likely to be diagnosed with ASD (95% CI: 2.85, 6.84).

What the researchers fail to acknowledge is that more healthcare visits mean more opportunities for developmental assessments and, therefore, more chances for diagnoses. This correlation has nothing to do with vaccines themselves.

• Vaccinated children are more likely to engage with healthcare systems and receive regular checkups, increasing the likelihood of developmental screenings and diagnoses.

• Conversely, unvaccinated children often have fewer medical visits, which may lead to underdiagnosis of developmental disorders.

This oversight—known as healthcare utilization bias—is a fundamental flaw that completely invalidates the study’s conclusions.

Methodological Shortcomings and Data Limitations

The study’s observational design and reliance on claims data introduce several additional issues:

• Observational nature: Correlation does not equal causation. The study does not establish a direct link between vaccines and NDDs but merely observes associations that could be driven by unmeasured confounding factors, such as family history, parental age, and genetic predispositions.

• Claims data: Medicaid claims are primarily collected for billing purposes and may misclassify vaccination status or developmental diagnoses. The study also failed to analyze the types, timing, or combinations of vaccines, making its conclusions overly simplistic.

The Narrow Scope of the Study Population

The study exclusively examined children enrolled in Florida Medicaid, focusing on low-income families with continuous Medicaid coverage for nine years. While this might seem comprehensive at first glance, this population selection introduces significant limitations that undermine the study's generalizability and credibility.

• Unrepresentative Sample: By limiting the analysis to Medicaid-enrolled children, the findings cannot be extrapolated to the broader population, which encompasses diverse socioeconomic, geographic, and healthcare access backgrounds. Medicaid populations often face unique challenges that are not reflective of the general population.

• Confounding Variables: Factors commonly associated with lower socioeconomic status—such as limited healthcare access, higher exposure to environmental toxins, and chronic parental stress—can independently increase the risk of neurodevelopmental disorders (NDDs). Additionally, in my experience as a Medicaid provider, family histories of NDDs often go undiagnosed in this population due to healthcare barriers. These undiagnosed cases create a bias in the data, as the familial predisposition to NDDs is not accounted for.

Cherry-picking a vulnerable group without properly adjusting for its unique challenges doesn't make the findings stronger; it makes them weaker and less credible.

Preterm and NDD connection?

Preterm birth is a risk-factor for neurodevelopmental disorders (NDDs), including autism and developmental delays, due to factors such as immature brain development, perinatal complications, and higher medical needs. The observed association between vaccination and NDDs in preterm children is likely explained by their increased healthcare engagement, which leads to more frequent developmental screenings and earlier diagnoses, not by the vaccines themselves. This phenomenon, known as healthcare utilization bias, falsely inflates the correlation between vaccinations and NDDs. Decades of rigorous research have consistently shown that vaccines do not cause NDDs, even in high-risk populations like preterm children. Further studies could clarify the interplay between prematurity, medical care, and NDD risk while continuing to affirm the safety and necessity of vaccines.

Contradictions with Established Research

This study’s findings conflict with decades of robust research showing no link between vaccines and autism. For example, A meta-analysis involving over 1.25 million children conclusively found no association between vaccines and ASD.

The stark contrast between this study and the broader scientific consensus underscores its limitations and biases.

What a Better Study Would Look Like

1. Study Design: Use a prospective cohort design to follow children from birth, capturing data on vaccinations, timing, and health outcomes over time. Randomized trials are not ethical, but observational comparisons between fully vaccinated, partially vaccinated, and unvaccinated groups could work.

2. Diverse Population: Include children from various socioeconomic, racial, and geographic backgrounds, and recruit participants from both Medicaid and private insurance to ensure generalizability.

3. Comprehensive Data Collection: Gather detailed information on vaccine types, doses, and timing, along with standardized developmental assessments, family health history, parental age, and environmental factors.

4. Control for Confounding Variables: Statistically account for factors like family history of NDDs, socioeconomic indicators, environmental exposures, healthcare access, and changes in diagnostic criteria.

5. Avoid Healthcare Utilization Bias: Compare developmental screenings across all children regardless of the number of medical visits to distinguish vaccination effects from healthcare engagement.

6. Large Sample Size and Long Follow-Up: Enroll tens of thousands of children and follow them through key developmental milestones to detect patterns and avoid survivorship bias.

7. Transparent Publication: Publish in a high-impact, peer-reviewed medical journal with robust ethical oversight to ensure credibility.

By implementing these steps, a study would produce more reliable, generalizable, and trustworthy conclusions about vaccines and neurodevelopmental outcomes.

But guess what, this has been done before. MANY times. HERE:

1. Taylor et al. (2014) – Systematic Review and Meta-Analysis

This meta-analysis comprehensively reviewed 10 high-quality studies involving over 1.25 million children to investigate the relationship between vaccinations and autism. The analysis included studies from various countries, ensuring a diverse and representative population sample. Data were extracted from large-scale cohort and case-control studies, providing robust insights. Importantly, the included studies accounted for confounding factors such as demographic variables and family history, ensuring the findings were not biased by these variables. The meta-analysis found no evidence of a link between vaccines and autism or autism spectrum disorders, reinforcing the safety of vaccines. This research was published in the journal Vaccine, a well-respected, peer-reviewed publication in immunization research.

Read the study here: Taylor et al., 2014 - Vaccine and Autism Meta-Analysis

2. Hviid et al. (2019) – Nationwide Cohort Study in Denmark

This large-scale cohort study followed 657,461 children born in Denmark over a decade, examining the potential association between the MMR vaccine and autism. The study leveraged a nationwide dataset, ensuring a diverse and comprehensive sample. Detailed data were obtained from Danish population registries, including vaccination records and autism diagnoses. The researchers carefully adjusted for numerous confounding factors such as child’s age, sex, birth year, maternal and paternal age, socioeconomic status, and parental psychiatric history. Their findings showed no increased risk of autism associated with the MMR vaccine, even among children at higher risk for the condition. This rigorously conducted research was published in the Annals of Internal Medicine, a highly respected, peer-reviewed medical journal.

Read the study here:Hviid et al., 2019 - MMR Vaccine and Autism

Conclusion

It’s exhausting to continually refute studies like this, but it’s necessary. The anti-vaccine community’s celebration of such flawed research speaks volumes about their misunderstanding of scientific rigor. Instead of advancing meaningful conversations, they cling to poorly executed studies to justify their narratives, often ignoring the glaring issues with methodology and bias.

This behavior erodes public trust in science and risks fueling vaccine hesitancy, which can lead to outbreaks of preventable diseases.

Why the anti-vaccine community refuses to listen is something we may never truly understand. They claim to seek "truth," but their endless cycle of repetitive claims and flawed studies suggests they’re more interested in perpetuating doubt than finding answers. These tactics follow the same old playbook: cherry-picking questionable studies, amplifying discredited voices, and sowing fear—all while ignoring mountains of high-quality, evidence-based research.

This recent study, published in a questionable journal and heavily promoted by anti-vaccine advocates, is yet another example of this strategy. It’s not groundbreaking, nor does it prove anything. Its deeply flawed methodology, unrepresentative population, and failure to account for even the most basic confounding factors render its conclusions utterly unreliable.

As pediatricians and healthcare professionals, we dedicate our lives to the health and well-being of children. Vaccines remain one of the safest, most effective tools we have to protect them. This isn’t an opinion—it’s the consensus of decades of rigorous, high-quality research. Yet here we are again, explaining the same truths to those who refuse to hear them.

The stakes are too high to let bad science and propaganda drive the conversation. Misinformation costs lives, and our job—whether as parents, advocates, or professionals—is to counter it with facts, logic, and unwavering empathy. We care about your children’s health. That’s why we speak up, even when it feels like shouting into the void.

So, to the anti-vaccine movement: What are you really searching for? And if it’s truth, why do you keep looking in all the wrong places?

On The PDT Podcast

My daughter struggled with diaper rash after diaper rash until I switched her to Coterie diapers. Diapers are on our babies’ sensitive skin 24/7 and finding a product that is high-quality, clean and safe will ensure their skin health.

This week, I welcome Jess Jacobs, the CEO of Coterie, to discuss a healthy skin care routine for your baby and how Coterie’s innovative brand challenges industry norms by consistently exceeding expectations in product safety and performance. 

She joins me to discuss:

• Coterie’s commitment to offering high-quality, clean and safe products designed to alleviate worries for parents

• Her personal experiences as a mother including her kids’ sensitive skin issues

• That it is important for brands to set a high standard for their products and to empower parents with clear and straightforward education about skin health

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• Language vs. communication

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• When to seek help…AND MORE!

Ask Dr. Mona

An opportunity for YOU to ask Dr. Mona your parenting questions!

Dr. Mona will answer these questions in a future Sunday Morning Q&A email. Chances are if you have a parenting concern or question, another parent can relate. So let's figure this out together!