RFK Jr. is misrepresenting a landmark Danish study that followed 1.2 million children over 24 years. The study found no link between aluminum in vaccines and autism or neurodevelopmental harm. Let’s fact-check his claims - using actual data. 🧵
2/ This study represents gold-standard epidemiological research. Over 24 years, researchers tracked 1.2 million children across 50 health outcomes. Edward Belongia, leading vaccine safety expert: "the largest and most definitive observational study on the safety of vaccine-related aluminum exposure in children" ever conducted. pubmed.ncbi.nlm.nih.gov/40658954/
3/ RFK Jr. claims the study was "designed not to find harm." That’s wrong. Different birth cohorts received different aluminum doses due to national policy changes - not parental choice. This “natural experiment” minimizes confounding and bias. It’s a strength, not a flaw.
4/ RFK Jr.'s central claim is demonstrably false: he cites "67% increased Asperger's risk" from supplementary data.
The actual study shows Asperger's HR 1.13 (0.89-1.44), which is not statistically significant and nowhere near 67%. In extended follow-up: HR 1.02 (0.93-1.12). Not sure where 67% came from.
5/ He calls exclusions “deceptive,” but they’re standard epidemiology. Excluding children who died before age 2 or had serious pre-existing illness avoids confounding. Excluding "implausible" vaccine doses is routine data cleaning - flagging registry errors, not hiding evidence.
6/ The aluminum safety record is robust: WHO's Global Advisory Committee found "no evidence of health risk in >60 years of use" across >1 billion doses. This conclusion isn’t based on one study, it’s consistent across decades of research.
7/ The Danish study specifically found no increased asthma risk with aluminum exposure (HR 0.96, CI 0.94-0.98). While a 2023 U.S. study suggested a small potential association, its authors stressed it was observational, couldn't prove causation, and benefits vastly outweigh any unproven risks. pubmed.ncbi.nlm.nih.gov/36180331/
8/ RFK Jr. calls it “absurd” that higher aluminum exposure was linked with lower disease risk in some outcomes. But that’s a known phenomenon: residual confounding in observational studies. It doesn’t mean aluminum is protective - just that real-world data is complex.
9/ He accuses the researchers of corruption.
In fact:
- The study was not funded by industry
- @SSI_dk is a public health institute - not a pharma company
- Data sharing limits stem from Danish privacy law
This is not a cover-up. It's standard scientific protocol.
10/ RFK Jr. fabricates statistics (that "67% risk" doesn't exist, as far as I could tell), misrepresents routine methods as "deception," and levels baseless accusations of fraud. That's not scientific critique. It's misinformation. Parents deserve facts, not fear. /end
Thanks to an astute colleague for pointing out where the '67%' figure came from: it's from one tiny subgroup in the supplementary data (Supplement Figure 4), just 51 Asperger cases from one birth cohort (2007-2018).
This is textbook cherry-picking, and here's why it's misleading:
The finding is barely significant with a confidence interval of 1.01-2.77. That wide range means the true effect could be anywhere from a 1% increase to nearly tripling the risk, massive uncertainty from small numbers.
The earlier birth cohort (1997-2006) with 124 cases, 2.5 times more data and longer follow-up, shows HR 0.99 (0.76-1.29), completely non-significant. If aluminum caused Asperger's, we'd see consistent effects across cohorts.
Most damning: the exact same data shows autism spectrum disorder HR 0.91 (0.87-0.96) and autistic disorder HR 0.92 (0.86-0.98), statistically significant protective effects with thousands more cases. If I cherry-picked like this, I could claim "aluminum prevents autism!" But that would be equally dishonest.
This is why you don't mine subgroup analyses. When you run hundreds of comparisons, some will hit significance by chance. The overall pattern shows no evidence aluminum in vaccines causes autism or neurodevelopmental harm. acpjournals.org/doi/suppl/10.7…
P.S. I understand why people ask about unvaccinated controls - it seems logical on the surface.
But here's why the Danish study's design is actually more scientifically robust:
The study did include 15,237 children who received no aluminum-containing vaccines by age 2. To test whether including this small unvaccinated group affected their results, researchers ran a separate analysis that excluded these children entirely - looking only at vaccinated children with varying aluminum exposures. The findings were unchanged, confirming that the presence of unvaccinated children didn't bias the results.
But comparing vaccinated vs unvaccinated creates major problems: Unvaccinated families differ systematically from vaccinated ones in healthcare-seeking behavior, socioeconomic factors, lifestyle choices, and attitudes toward medical intervention. These differences make it nearly impossible to tell if any health differences are due to vaccines or these other factors.
There's also an ethical issue: researchers can't randomly assign children to remain unvaccinated when vaccines are the standard of care and prevent serious diseases. That would be like withholding known effective treatments.
Denmark's study is actually more sophisticated: over 24 years, Denmark's national vaccine program naturally evolved - they introduced new vaccines, switched suppliers, and updated formulations for routine public health reasons. This created different aluminum exposure levels across birth cohorts without any intentional experimentation. This 'natural experiment' lets researchers compare low vs medium vs high aluminum exposure within a vaccinated population - avoiding the confounding problems of vaccinated vs unvaccinated comparisons. This dose-response approach across 1.2 million children with careful statistical controls is robust epidemiological methodology.
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As an infectious diseases physician and vaccine specialist, I need to address several serious misrepresentations, baseless assertions, and factual errors in this post. 🧵
1/ Calling mRNA vaccines “genetic ‘vaccine’ products,” with “vaccine” in quotes, is a deliberate rhetorical move that undermines their legitimacy.
These are real vaccines by every scientific and regulatory standard. They generate protective immunity, prevent severe disease, and have saved millions of lives. The mRNA remains in the cytoplasm, never enters the nucleus, and is rapidly degraded within hours, providing temporary instructions for cells to make a harmless viral protein that stimulates protection. cdc.gov/covid/vaccines…
2/ The claim that “vaccines would never be the answer to an ongoing viral outbreak” ignores public health history. Vaccines were central to smallpox eradication, polio near-eradication, and the rVSV-ZEBOV (Ervebo) vaccine was instrumental in controlling later Ebola outbreaks in the DRC. cidrap.umn.edu/ebola/study-du…
If anyone claims vaccines haven’t been properly studied, show them this:
We’ve now logged 500 randomized, controlled vaccine trials into our dataset with ~7.2M participants. The vast majority of trials reported safety outcomes. Many more trials to come. bit.ly/4le8z7D
Huge thanks to the inspiration and co-leader of the project, @BradSpellberg, and to our amazing team of volunteers who have been putting many hours into this - @AliSMV7, @alejodiaz81, @DhandAbhay, @ThePharmFox, @zacroBID, @TravisBNielsen, Dr. Matthew Phillips, @SarahRawi1, @IDwithNWD, Dr. Kusha Davar, Dr. Devin Clark, and countless anonymous contributors.
And beyond those 500 trials with 7.2 million participants, vaccine safety doesn't stop at licensure.
Monitoring continues throughout each vaccine's lifecycle through a multi-layered surveillance system designed to detect rare or delayed reactions that even massive trials can miss.
In the U.S., this monitoring begins with VAERS, an early-warning system that allows anyone (patients, providers, or manufacturers) to report health events following vaccination. But while VAERS can highlight patterns, it doesn't establish causality.
That's where the Vaccine Safety Datalink (VSD) comes in. By linking electronic health records for millions of people across integrated health systems, the VSD allows researchers to compare outcomes in vaccinated and unvaccinated populations in near real time. When VAERS signals a concern, these databases help determine whether there's truly an increased risk.
COVID-19 vaccination put this infrastructure to the test. With hundreds of millions of doses administered, the system identified rare events like myocarditis and thrombosis with thrombocytopenia syndrome, sometimes affecting fewer than 10 people per million doses. The key was early detection and rapid investigation by the surveillance system.
This level of surveillance is unprecedented in medicine. Combined with rigorous pre-licensure trials, it forms one of the most robust safety monitoring systems in all of healthcare.
1/ Tucker Carlson: “Do you think overall the COVID vaccine killed more people than it saved?”
RFK Jr: “The truth is, I don’t know.”
This is outrageous.
I do know.
The answer is: unequivocally no. 🧵
2/ RFK Jr then added:
“And the reason I don't know is because the studies that were done by my agency were sub-standard, and they were not designed to answer that question."
I cared for hundreds of COVID patients and watched far too many die - including young, relatively healthy adults who never had a chance to get vaccinated, or who declined it.
And I’ve reviewed the evidence. Many of the studies he’s dismissing are anything but “sub-standard.”
It’s not even close.
3/ Before vaccines, ICUs were overwhelmed. Hallways filled. Some hospitals had to triage patients - deciding who might receive care and who wouldn’t. The suffering was unlike anything any of us had seen in our careers.
Then vaccines arrived. Deaths plummeted. By mid-2021, nearly every fatal case was among the unvaccinated. That pattern held across hospitals and regions.
2/ Research shows that many Amish families do vaccinate their children. Studies find that anywhere from 41% to 85% of Amish parents have vaccinated at least some of their children, depending on the community and time period.
3/ The historical record also tells a very different story about health outcomes. The last U.S. polio outbreak, in 1979, occurred in unvaccinated Amish communities and resulted in 15 cases, including 10 with paralysis. A 1991 rubella outbreak among the Amish led to at least 10 babies born with congenital rubella syndrome, suffering heart defects, deafness, and blindness. And in 2014, the largest measles outbreak in the U.S. in over two decades infected 383 people, nearly all of them Amish, after unvaccinated missionaries returned from overseas.
These outbreaks didn’t resolve on their own. They were halted through large-scale emergency vaccination campaigns, often with active participation from Amish leaders and parents once the risks were clearly understood.
RFK Jr's thimerosal thread is a masterclass in misinformation. Let's fact-check it line by line. 🧵
2/ CLAIM: “There are high bolus doses of mercury in flu shots.”
FACT: 96% of flu vaccines are thimerosal-free.
Multi-dose vials contain 25 mcg per dose. That’s not a “high bolus.” fda.gov/vaccines-blood…
3/ CLAIM: "A compliant child could get 500 µg of ethylmercury."
FACT: This is mathematically impossible. Today’s formulations can’t reach that total. Multi‑dose flu vials hold 25 µg each. A child vaccinated every season from 6 months to 18 years (19 doses) would max out at 475 µg - and that assumes every dose came from a multi‑dose vial. But only about 4% of the U.S. flu‑shot supply for 2025‑26 is multi‑dose; single‑dose syringes are standard for kids. Realistic lifetime exposure is therefore a small fraction of 500 µg.
It’s not easy to navigate the maelstrom of misinformation. Grateful to @megtirrell and @boulware_dr for cutting through it.
Slides prepared for ACIP this week by former CHD leader Lyn Redwood cited a 2008 Neurotoxicology study on thimerosal and “long-term brain harm.”
But the study doesn’t exist. The listed author says he never wrote it and his actual research found no such effect.
Debates should be grounded in evidence, not phantom citations.
Thimerosal has been thoroughly studied for decades. Here's what the evidence actually shows🧵👇 cnn.com/2025/06/24/hea…
2/ What the evidence actually says
Thimerosal has been used in vaccines and biologics since the 1930s. It’s highly effective at killing bacteria and preventing contamination, especially in opened multi-dose vials.
Thimerosal contains ethylmercury, not methylmercury. Ethylmercury is broken down and excreted quickly; unlike methylmercury, it doesn’t build up or persist in the body.
In 1999, U.S. health agencies recommended removing thimerosal from childhood vaccines as a precaution, not because of evidence of harm. By 2003, all thimerosal-containing pediatric vaccines (except some flu shots) had expired. pubmed.ncbi.nlm.nih.gov/10418806/
3/ Today, most flu shots are thimerosal-free.
Only multi-dose vials contain it, for practical storage reasons.
FDA: fda.gov/vaccines-blood…