Why a study claiming vaccines cause chronic illness is severely flawed – a biostatistician explains the biases and unsupported conclusions
At a Senate hearing on Sept. 9, 2025, on the corruption of science, witnesses presented an unpublished study that made a big assertion.
They claimed that the study, soon to be featured in a highly publicized film called “An Inconvenient Study,” expected out in early October 2025, provides landmark evidence that vaccines raise the risk of chronic diseases in childhood.
The study was conducted in 2020 by researchers at Henry Ford Health, a health care network in Detroit and southeast Michigan. Before the Sept. 9 hearing the study was not publicly available, but it became part of the public record after the hearing and is now posted on the Senate committee website.
At the hearing, Aaron Siri, a lawyer who specializes in vaccine lawsuits and acts as a legal adviser to Secretary of Health and Human Services Robert F. Kennedy Jr., said the study was never published because the authors feared being fired for finding evidence supporting the health risks of vaccines. His rhetoric made the study sound definitive.
As the head of biostatistics at the University of Pennsylvania’s Perelman School of Medicine, when I encounter new scientific claims, I always start with the question “Could this be true?” Then, I evaluate the evidence.
I can say definitively that the study by Henry Ford Health researchers has serious design problems that keep it from revealing much about whether vaccines affect children’s long-term health. In fact, a spokesperson at Henry Ford Health told journalists seeking comment on the study that it “was not published because it did not meet the rigorous scientific standards we demand as a premier medical research institution.”
The study’s weaknesses illustrate several key principles of biostatistics.
Study participants and conclusions
The researchers examined the medical records of about 18,500 children born between 2000 and 2016 within the Henry Ford Health network. According to the records, roughly 16,500 children had received at least one vaccine and about 2,000 were completely unvaccinated.
The authors compared the two groups on a wide set of outcomes. These included conditions that affect the immune system, such as asthma, allergies and autoimmune disorders. They also included neurodevelopmental outcomes such as attention-deficit/hyperactivity disorder, or ADHD, autism and speech and seizure disorders, as well as learning, intellectual, behavioral and motor disabilities.
Their headline result was that vaccinated children had 2.5 times the rate of “any selected chronic disease,” with 3 to 6 times higher rates for some specific conditions. They did not find that vaccinated children had higher rates of autism.
The study’s summary states it found that “vaccine exposure in children was associated with increased risk of developing a chronic health disorder.” That wording is strong, but it is not well supported given the weaknesses of the paper.
Timeline logic
To study long-term diseases in children, it’s crucial to track their health until the ages when these problems usually show up. Many conditions in the study, like asthma, ADHD, learning problems and behavior issues, are mostly diagnosed after age 5, once kids are in school. If kids are not followed that long, many cases will be missed.
However, that’s what happened here, especially for children in the unvaccinated group.
About 25% of unvaccinated children in the study were tracked until they were less than 6 months old, 50% until they were less than 15 months old, and only 25% were tracked past age 3. That’s too short to catch most of these conditions. Vaccinated kids, however, were followed much longer, with 75% followed past 15 months of age, 50% past 2.7 years of age and 25% past 5.7 years of age.
The longer timeline gave the vaccinated kids many more chances to have diagnoses recorded in their Henry Ford medical records compared with the nonvaccinated group. The study includes no explanation for this difference.
When one group is watched longer and into the ages when problems are usually found, they will almost always look sicker on paper, even if the real risks are the same. In statistics, this is called surveillance bias.
The primary methods used in the paper were not sufficient to adjust for this surveillance bias. The authors tried new analyses using only kids followed beyond age 1, 3 or 5. But vaccinated kids were still tracked longer, with more reaching the ages when diagnoses are made, so those efforts did not fix this bias.
