Mailbag: Debunking Vaccines Myths

Welcome to Healthcare Rounds, where we give you smart conversations with the people moving healthcare forward. I'm John Marchika, CEO of Darwin Research Group. Today's mailbag is about healthcare misinformation, disinformation, and vaccines. Last week, at the end of the episode with Larry Levitt, I mulled out loud over the idea of doing an episode myself on the issue and decided to put today's episode together. As a reminder, if you have a question or comment for me, please send it to HealthcareRounds at DarwinResearch.com. And if you're not receiving Darwin's weekly newsletter, you can subscribe at DarwinResearch.com. It used to be that there wasn't much of a question about vaccines. It was just something you got when you were a kid, or you did for your own kids without thinking. Or maybe if you were traveling to certain countries abroad or if you joined the military, you got the necessary shots. But these days everyone seems to have an opinion on vaccines, and that's largely because of COVID, I'd say. I was one of those people loudly encouraging everyone I knew to get the vaccine as soon as it was available. But an unexpected consequence of those dark years was an emerging general vaccine hesitancy among a small but growing percentage of the population. And an even larger percentage of Americans was showing signs of increased skepticism and distrust of institutions, including science. Now, Gallup has studied trust in institutions for decades, and there's a common pattern. It's declining everywhere. The why behind this trend is a bigger topic than we can cover here, but with a little Googling, you'll find lots of opinions and even, dare I say, research studies on declining institutional trust. If you're interested, you'll find a link in the show notes to the Gallup page on trust, where you can see the data for yourself. And that brings me to the CDC. For most of my life, the Centers for Disease Control and Prevention has been the pinnacle, the gold standard or the creme de la creme of public health authorities. In fact, at different times during my career, one of my go-to newsletters has been the CDC's own weekly mortality and morbidity report. Well, what's been happening at the CDC writ large is a topic for another day, but I want to focus on one specific thing or event as it relates to vaccines. Back in November, the CDC quietly rewrote one of its own web pages to cast doubt on a question medical science settled years ago, whether vaccines cause autism. A handful of outlets covered it when it happened, but then it kind of faded from memory. The broader question we should all be thinking about is this. When the federal agency responsible for public health itself becomes a source of misinformation and disinformation, what are we supposed to do about that? As physicians, as researchers, as patients, or as parents? I'll eventually get to answering that question here, but for now I'd like to address the issue head-on. What we know about the link between vaccines and autism, or as it's referred to now, and I'll be using these terms interchangeably, autism spectrum disorder, or ASD. Let's start with some facts. Fact one, the overwhelming conclusion among researchers who have studied the vaccine autism link is that autism is not caused by or correlated with or linked to vaccines. And specifically I'm referring to the measles, mumps, and rubella vaccine, or MMR, which is given in two doses in early childhood. Other issues that encircle vaccines, like the safety and efficacy of the COVID vaccine, or the safety of adding preservatives to vaccines, have also been studied extensively, but that's not our focus here. Fact two The reason why this is the consensus view by a mile is not because of beliefs or opinions, it's because of evidence. And this is not a thin body of evidence. The link between the MMR vaccine and autism is one of the most heavily studied questions in modern medicine, and it's been answered repeatedly at massive scale by different research teams in different countries using different methods. For instance, in 2002, a Danish retrospective cohort study published in the New England Journal of Medicine included all children born in Denmark from 1991 to 1997, some 530,000 children, and found, quote, no association between the age at the time of vaccination, the time since vaccination, or the date of vaccination and the development of autistic disorder. In another study in 2014, a meta-analysis in the Journal of Vaccine pooled the data across more than 1.2 million children and found no link between vaccines and autism spectrum disorder. And third, a 2015 JAMA retrospective cohort study of 95,000 children with older siblings with and without autism concluded that the receipt of the MMR vaccine was not associated with increased risk of autism, regardless of whether older siblings had autism. And finally, in 2019, another Danish cohort study, this one covering more than 650,000 children, and published in the Annals of Internal Medicine, found no association, and I'll just read you their conclusion. Quote: The study strongly supports that MMR vaccination does not increase the risk for autism, does not trigger autism in susceptible children, and is not associated with clustering of autism cases after vaccination. It adds to previous studies through significant additional statistical power and by addressing hypotheses of susceptible subgroups and clustering of cases. Fact three. The notion that the MMR vaccine causes autism began with a paper published in 1998 that no one, excuse me, almost no one, believes to be credible today. That year, a British surgeon named Andrew Wakefield published the paper, labeled as an early report in the Lancet, claiming a link between the MMR vaccine and a new syndrome of autism and bowel disease. The hypothesized mechanism, according to Wakefield, was that the live measles component of the vaccine lingered in the gut, causing inflammation that let harmful proteins reach the brain. A quote, leaky gut theory that's really since been thoroughly discredited. Now, before I get what happened to Wakefield, I want you to consider the sample size. The study included a total of twelve children. That was the entire sample. Twelve. And that's probably why the editors at The Lancet flagged it as an early report. But aside from the sketchy science behind the leaky gut theory after the publication of the paper, it was revealed that Wakefield had been paid by lawyers who were building a lawsuit against vaccine manufacturers, money he never disclosed. Worse, Wakefield had altered patient data to manufacture the appearance of a link that wasn't there. In other words, he faked the data. So in 2010, Britain's general medical counsel found him guilty of serious professional misconduct and revoked his medical license. Hillancett fully retracted the paper the same year. If you're interested in the full story, there's a great book called The Doctor Who Fooled the World by investigative journalist Brian Deere. Fact four. You might know that over the last year and a half, Measles cases are climbing in the US. For context, in the decade before the first vaccine was introduced, back in the 1950s, we averaged about 500,000 reported cases per year, 48,000 hospitalizations, and about 400 to 500 deaths per year. But by 2000, when cases were declared eliminated in the US, there were 85 cases, and no hospitalizations or deaths. Recently, according to CDC data from 2021 to 2024, there were 49 cases, 121 cases, 59 cases, and 285 cases respectively, and there were no reported deaths over this time period. In 2025, however, there were 2,289 confirmed cases, and so far, through mid-July 2026, there have been 2,318 cases. That suggests we'll end up with about 5,000 cases by the end of the year if the trend continues. There have been three confirmed deaths reported by the CDC in the last 18 months, plus a fourth confirmed separately by the LA County Department of Public Health. Now over the years we've seen a few outbreaks in different parts of the country, with the largest being in 2019 in New York. This particular time period may be no different in the sense that the numbers are largely attributed to outbreaks in specific regions with low vaccination rates. But what is different is that we're clearly seeing a trend. Cases rose roughly eightfold from 2024 to 2025. And as I said, we're on pace to roughly double that again in 2026. When I first started working on this mailbag question, I intended to go through the CDC page on vaccines and autism line by line, pointing out errors and omissions and highlighting the fallacious arguments being used by the authors of the webpage. I tried that, and I promise you it's not an exercise built for a podcast. But I do encourage you to visit the page and see for yourself. The link is in the show notes. You don't have to take my word for it. There's an independent project called Restored CDC Org that preserves the page exactly as it read before the rewrite. First, quote, studies have shown that there is no link between receiving vaccines and developing autism spectrum disorder, end quote. Second, quote, no links have been found between any vaccine ingredients and ASD, end quote. If you don't trust an outside group to show you the page that once existed, you can also pull the same snapshot from the Internet Archives Wayback Machine, although it does require a little extra work. Again, to make it easy for you, I've included links to every study and every web page I reference in the show notes. The question you should be asking is, what changed? After what seemed to be settled science, agreed upon by researchers and pediatricians and medical societies and the CDC itself, and all these studies, why did the website change? After all, you would expect that a public health agency would revise its policy position when confronted with new information and better data. So again, what changed? What new data became available? As I've said before on this show, I always try to keep politics out of our work, but in this case it's unavoidable. The truth is, changing the webpage wasn't a career scientist decision, or a panel at the CDC. According to CDC leadership who spoke to Stat News, the CDC's own developmental disability experts, the people who work on autism research, weren't consulted before the page changed. And Secretary Robert F. Kennedy Jr. told the New York Times, in his own words, that he personally ordered the rewrite. This isn't a leak or an allegation, it's his own account of what happened. Kennedy spent two decades building a following in anti-vaccine and wellness spaces before he ever held office. And since taking over HHS, he's brought several of those longtime activists in-house to review vaccine safety. This is public knowledge. So I'm not telling you this to villainize anyone or take a political viewpoint. I'm telling you because what's on the CDC page wasn't the output of a scientific review process. It was a decision made by one person who's held this exact view publicly for a very long time, now with the authority to put it on a government website. I'll come back to this point in a moment. But as an exercise, I rewrote a short version of what the page should say based on the evidence, and it goes something like this. For many years the public has questioned whether the NMR vaccine is linked to autism. Here's the honest answer. We can say with full confidence it isn't. However, we know many parents are concerned with what appears to be a rise in autism cases. The CDC believes that autism prevalence has risen for three primary reasons. First, the diagnostic criteria broadened. In 2013, the diagnostic manual folded separate diagnoses, Asperger syndrome, and a catch all called pervasive developmental disorder into one umbrella, autism spectrum disorder. Because we've expanded the definition of autism, we're recording more cases. Second, screening became universal. Starting in 2007, pediatricians began screening every child at 18 and 24 months, whether or not anyone had raised a concern. Before that, a child usually wasn't evaluated until symptoms forced a referral, so milder cases went uncounted. And third, for decades, kids we now call autistic were labeled instead with intellectual disability or a general learning disability, often because that's the category schools had resources to deal with. As autism became its own recognized diagnosis with dedicated resources, that population shifted labels. Studies find autism diagnoses, studies find autism diagnoses rising in a school system, while intellectual disability diagnoses fall by a comparable amount, exactly what you'd expect if kids were being recounted and not newly affected. Vaccines are one of the best tools in medicine for preventing illness in a variety of conditions and diseases, including measles. Please talk to your doctor about all the appropriate vaccines that are necessary for your child's health and well-being. The gap between what I just read and what the current CDC page says does have something to do with science, but not in the way that you might think. I believe that the new web page exploits the public's lack of understanding of how science works. Now I said I wasn't going to walk you through the whole page, and I won't. But here's an example of what I'm talking about. Right at the top of the page, the first key point, the one that most people will read and remember, says this quote, the claim vaccines do not cause autism is not an evidence-based claim because studies have not ruled out the possibility that infant vaccines cause autism, end quote. Now that's ridiculous on his face. And then you get to the second bullet that says health authorities have ignored studies that support a link. That's simply not true, as I just four massive peer-reviewed studies. But about that claim not being evidence based? As most of you know, but about that claim not being evidence-based? Science doesn't work by proving things true. It works by proposing an explanation and then trying as hard as possible to prove that explanation wrong. You form a hypothesis, you design a test that can fail, and if it survives repeated attempts to falsify it, especially by other scientists trying to find the same results, your confidence in it grows. That's it. That's the whole scientific method. A finding that can't be tested and can't possibly fail isn't a scientific claim in the first place. It's something else. Let's call it a belief. Science deals in confidence, not certainty. And confidence increases over time through consensus as the evidence increases. So when the CDC's own page says studies, quote, have not ruled out the possibility, end quote, that's not a gap in the evidence. It's the ordinary condition of all scientific knowledge because you never really truly rule things out. The people who wrote that sentence understand this distinction perfectly well, but they're relying on a general public that doesn't. It's semantics and play. And speaking of confidence, remember those four studies that I cited earlier? The first reason to be confident is the quality of the journals themselves. Now, even the best journalists make mistakes, as we saw from the Lancet, but it's a pretty good indication of the quality of the research. Second, look at the sample sizes, 95,000, 530,000, 650,000, and 1.2 million. They're huge by any standard. Compare those to the COVID vaccine trials, which for the Pfizer and Moderna vaccines were 44,000 and 30,000 people, respectively. Or the phase three clinical trials, the last step before a drug is approved, that are required to prove that a drug works and that it's safe, which average around 5,000 people. There's a wide range that can be as few as 300 in rare disease cases, or maybe in 10 or 20,000 for larger populations. Or the opinion polls that you see on presidential approval ratings, of which the best ones are around 2,500 people. Now, on vaccines and autism, has this relationship been tested rigorously, repeatedly at scale by different research teams? What does the evidence show? How much confidence do you have in those data? I think by now you know where I stand on this point. The issue of healthcare misinformation and disinformation has been of interest to me throughout my career. And to understand why, I thought I'd share a little bit about my background. I studied economics at Knox College and went on to get an MBA and a master's in public policy at the University of Chicago. After starting my professional career at Abbott, I started a company called Faxwatch. And really the gist of what we did was to vet the most important medical research, summarize it, and then distribute it to physicians and other healthcare professionals. I left Faxwatch to pursue a PhD at the Dartmouth Institute, where I studied health economics, health policy, and clinical epidemiology. As I've mentioned several times on this show, my time at Dartmouth was sort of my personal foundation for starting Darwin Research Group in 2010. Throughout my time in the PhD program, I spent a lot of time with data sets, and I learned at the very least how to write a decent abstract. But I also spent countless hours reviewing peer-reviewed studies and learned new powerful tools to evaluate the quality of those studies. It was kind of what I did at Faxwatch, but this was at a whole new level. Considering the backdrop of what I just told you about my background, here's the reality. I took science in high school, pretty much just the requirements like biochemistry and physics. And I studied Thomas Kuhn in college and all that normal science and paradigm shift stuff and Ptolemy and Galileo and Copernicus. None of it stuck. I didn't really start thinking scientifically, if you will, in any meaningful way until I was well into my 30s. The overwhelming majority of Americans got through high school and maybe college without choosing a career in science. They used to trust their family doctor for advice on things like whether and when to vaccinate their kids. But today, in our influencer and content creator culture, in a social media driven world, experts and expertise don't seem to matter as much. All the more reason for an institution like the CDC to get it right. Before COVID, vaccine hesitancy in this country was limited to a very small group of people within the wellness movement. Organic food, attachment parenting, distrust of pharmaceutical companies, and a general suspicion that modern medicine overintervenes. It was a lifestyle position, and it was concentrated among educated high income parents. They never encountered measles, really, because it had been eliminated for a generation. The disease had become invisible. Public health researchers call this attitude complacency because it just doesn't seem relevant anymore. Ask yourself the last time you thought about polio. But then COVID happened and vaccines stopped being a shared medical baseline and became a political fight almost overnight. That tangling of politics and public health is the backdrop for everything I want to say as I close this episode out. Here's where I land on that. Science needs to stay agnostic to politics, whichever direction the politics are pointing. The MMR autism question was settled by evidence, not by which party held the White House when the studies were published. The moment a government agency starts editing scientific conclusions to match a political appointee's prior beliefs, you've destroyed its independence, which in turn reinforces the cycle of distrust. Vaccine hesitancy is rarely pure ignorance. It's often a reasonable person responding to a genuine breakdown in trust. Sometimes trust in a pharmaceutical industry, sometimes trust in a doctor or an insurance company that hasn't listened to them, sometimes trust in institutions that, as this Very episode is shown, have in fact put out compromised information. The tragedy of the CDC autism page isn't just that it's wrong, it's that it hands ammunition to people whose distrust, in other respects, might have honest roots, and it burns whatever credibility CDC has left to reach them. So to sum up, here's the full story. We have a fraudulent 1998 paper that should have died with its retraction. We have a body of evidence since then about as large and consistent as public health research gets. We have a wellness culture on one end that never fully let the fraud go, a political movement on the other that gave it a megaphone, and a pandemic in between that taught an entire country to distrust its health agencies at the exact moment those agencies needed people to listen. And now we have a government website that is providing misinformation and disinformation to the public it's meant to serve. And as a result, we have a continued public erosion of trust and real-world public health consequences. And to answer the question, what are we supposed to do when the CDC itself becomes a source of misinformation and disinformation? I honestly don't know, other than to do what I'm doing right now. Take whatever voice I have and set the record straight for anyone who's willing to listen. For most of you listening, this isn't an abstract question either. If you work inside a health system or a drug manufacturer or a health tech company, you're already a trusted source for the people around you. Whether you ask for it or not, colleagues, family, and sometimes patients who want to know what you think because you work in healthcare. So know your primary sources. Read the study before you repeat the headline. And don't take my word for any of this either. Check the links yourself. I also want to address one final point, which is a lesson I learned a long time ago. Facts and logic don't move someone who's already emotionally committed to a position. They never have. And this episode was never really created for that person. It was built for you, the people navigating this erosion of trust professionally. But here's what I won't concede. Facts matter. Evidence matters. There's a real, knowable, tested answer to whether vaccines cause autism, and the people who rewrote that page know it. Someone with the training to tell good science from bad, the exact training I got in my first year of graduate school, sat down and chose to reframe settled science as unresolved, then reached for the same rhetorical tricks we spent this whole episode naming, because unresolved is more useful to them than true. I don't have patience for the idea that there's your truth and my truth here. There's what the evidence shows, and then there's everything else. And the everything else doesn't get to dress itself up as equally valid just because a once prestigious institution said so. If you enjoyed this episode, forward it to a friend and rate, review, and subscribe on your favorite podcast platform. If you have a question or comment from me, please send it to healthcare rounds at darwinresearch.com. I'm John Marchica. See you next round.