More and more routine vaccines are being linked to lower risks of dementia. Shots against seasonal flu, RSV, tetanus, diphtheria, and pertussis (Tdap), pneumococcal infections, hepatitis A and B, and typhoid have all been linked to lower risks. And one of the strongest connections is from vaccination against shingles, with more data supporting the link still coming in. But as the evidence mounts, scientists continue to puzzle over the pleasant surprise—how are vaccines that target specific pathogens inadvertently shielding our minds from deterioration?

A burgeoning hypothesis offers a brow-raising possibility: The shots may be protecting our noggins by training the part of our immune system that had long been considered untrainable. If the idea holds up, it could generate a deeper understanding of fundamental aspects of our immune systems while opening new avenues to treating or preventing dementia. It could also add another dimension to the benefits of vaccines, which already save millions of lives worldwide.

Trained immunity

It's well understood how vaccines work generally; they're designed to prime our immune systems against specific pathogens. Vaccines present either defanged pathogens or distinctive fragments of them to specialized immune cells—namely, T cells and antibody-producing B cells—that can then learn to identify those microbial enemies.

So if such a pathogen stages an attack after immunization, those immune cells will be able to recognize the invaders quickly and destroy them. This process, as intended, engages adaptive immune responses, the part of the immune system known to be trainable. It can learn to target specific threats—and remember those threats, aka immunologic memory.

Then there's the other part of the immune system, the innate immune responses. These precede adaptive responses, acting as first-line, non-specific defenses against germs and injury. Innate defenses include everything from physical barriers—skin, mucous, gastric acid—to immune cells that can indiscriminately gobble invaders, as well as chemical signals that can swiftly ignite generic inflammation.

For decades, the innate immune response was considered relatively static—not one that evolves or hones itself as new threats are encountered. But that changed in 2011 with the coining of the term "trained immunity" to explain changes documented in innate immune responses from past exposures. Trained immunity occurs when cells involved in innate responses are activated and then primed by generic signals from a germ. Those primed cells acquire and maintain changes that allow them to respond to those germ signals faster and with more intensity the next time they're encountered.

Specifically, the changes observed in trained immunity are epigenetic. These don't alter the underlying DNA sequence of the cells but are modifications or chemical tags that alter gene activity. In the case of trained immunity, the changes may involve genes coding for pro-inflammatory signals that make those genes more active when the same germ signal is encountered again. Ultimately, this would lead to a stronger inflammatory response. Similar to adaptive responses, these epigenetic changes stick around afterward, creating another type of immunologic memory.

Quirky vaccines

So how does this connect to vaccines? The concept of trained immunity was solidified by data involving a vaccine—but one that's far from routine in the US: the quirky Bacillus Calmette-Guérin (BCG) vaccine, which was designed to protect against tuberculosis, caused by the bacterium Mycobacterium tuberculosis, but also used to treat bladder cancer (it's still unclear how the vaccine works against this cancer).

Nevertheless, in 2012, researchers in the Netherlands conducted an experiment to investigate trained immunity in mice engineered to lack adaptive immune responses—they had no T cells or B cells. The researchers vaccinated the weakened animals with BCG, looking for changes in innate responses, the only responses the mice had.

The researchers found that the shot not only bolstered the rodents' innate protective responses against M. tuberculosis but also boosted responses against an unrelated yeast pathogen, Candida albicans. Further work suggested similar trained immunity occurred in humans.

In the same study, the researchers examined blood samples from healthy human trial participants before and after immunization with BCG. After vaccination, the researchers found that immune cells in their blood produced stronger innate responses (pro-inflammatory signals) to M. tuberculosis than they did before the shot. They also produced stronger responses to C. albicans and the bacterial pathogen Staphylococcus aureus, suggesting non-specific trained immunity. The study was published in PNAS.

Since then, researchers have built a body of evidence to support and understand trained immunity. But in the past few years, the idea has collided with a steady stream of large population studies that have found that vaccines seem to protect against dementia. While most of the big studies that have made headlines have focused on routine vaccines—shingles and the flu, for example, a study in 2023 found that the BCG vaccine is also associated with a significantly lower risk of dementia.

In March, vaccine researchers in Belgium and South Africa, led by Justin Devine, put the findings together, including all the work on BCG, and published a hypothesis: Perhaps trained immunity from vaccines is behind the lower risks of dementia.

Prior to this, a leading hypothesis for the connection was that vaccines reduce the risk of dementia directly by preventing infections that can lead to inflammation in the brain, which, over time, could cause deterioration. This is particularly a strong hypothesis for the shingles vaccine. Shingles is caused by the varicella-zoster virus, which initially causes chickenpox but then lingers in the body, staying mostly dormant in nerve cells. It can reactivate any time there's a fault in the immune system, which often happens in older age, when immune responses naturally wane.

A shot of a shingles vaccine blocks reactivation, potentially preventing the virus from triggering brain inflammation that could contribute to the development of dementia. Conversely, there's some evidence that having shingles may increase the risk of dementia.

A possible mechanism

But not every vaccine linked to reduced dementia risk comes with such an explanation for how it may protect the brain. For example, the seasonal flu vaccine seems to reduce dementia, but it's unclear how. Still, in a large retrospective study published last month, researchers again bolstered the link between the seasonal flu shot and lower risks of dementia, this time finding that high-dose seasonal flu shots given to older patients are yet more protective against dementia than standard doses.

In other words, there seems to be a dose-dependent response—the higher the flu vaccine dose, the lower the dementia risk. The authors don't speculate on how the seasonal shot could affect cognitive health, but they call for more research into potential mechanisms, including trained immunity.

In the March hypothesis piece, published in the journal Frontiers in Immunology, Devine and colleagues hypothesize that trained immunity from vaccinations could indeed be responsible.

"A central element in this immunological model is that uncontrolled or excessive levels of neuro-inflammation, associated with elevated dementia risk, can be counteracted by epigenetic reprogramming of innate immune cells," they write.

For instance, it may be that the nonspecific changes to innate responses from vaccines are able to keep both targeted and non-targeted pathogens in check, preventing brain inflammation from flaring up, they say.

For now, the idea is just a hypothesis, and there's a lot more work needed to validate it. But the stakes are high for pursuing it, the researchers argue. "Elucidating the mechanisms underlying these promising observations may open new avenues to promote healthy aging through vaccination and could be crucial for alleviating the global burden of dementia," they write.

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In recent years, many overworked doctors have turned to so-called AI medical scribes to help automatically summarize patient conversations, diagnoses, and care decisions into structured notes for health record logging. But a recent audit by the auditor general of Ontario found that AI scribes recommended by the provincial government regularly generated incorrect, incomplete and hallucinated information that could "potentially result in inadequate or harmful treatment plans that may potentially impact patient health outcomes."

In a recent report on Use of Artificial Intelligence in the Ontario Government, the auditor general reviewed transcription tests of two simulated patient-doctor conversations performed across 20 AI scribe vendors that were approved and pre-qualified by the provincial government for purchase by healthcare providers. All 20 of those vendors showed some issue with accuracy or completeness in at least one of these simple tests, including nine that hallucinated patient information, 12 that recorded information incorrectly, and 17 that missed key details about discussed mental health issues.

In the report, the auditor general points out multiple concerning examples of mistakes in those summaries that could have a direct and negative impact on a patient's subsequent care. That includes situations where an AI scribe hallucinated nonexistent referrals for blood tests or therapy, incorrectly transcribed the names of prescription medication, and/or missed "key details" of mental health issues discussed in the simulated conversations.

Across all approved vendors, the average tested AI scribe scored only a 12 out of 20 on the "accuracy of medical notes generated" section of Supply Ontario's evaluation rubric. But that seemingly key "accuracy" metric was only responsible for about 4 percent of a vendor's overall score, making it easy to meet the minimum threshold for approval even if an AI scribe scored a "zero" on the accuracy metric (a separate metric measuring "domestic presence in Ontario" was worth 30 percent of the overall scoring).

All these factors contributed to the auditor general's overall finding that these AI scribes "were not evaluated adequately." In a display of restraint and understatement, the report notes that "it is important that AI scribe systems are tested to provide assurances as to the quality of their generated notes and to minimize inaccuracies." It also recommends that IT departments using these scribes force doctors to "confirm their review of the notes produced" before committing them to patient logs.

Public sector health services in Ontario are not required to use these AI scribe systems in their work and may purchase scribes from non-approved vendors if they wish. Still, the fact that the Ontario government recommended AI summary systems with such obvious and potentially patient-harming flaws should give pause to any doctors (or their patients) making use of them.

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Beneath the low hum of interstate traffic punctuated by the treble of birdsong, Anne Marie Mozrall directs her team of researchers preparing to gather data on the troubling confluence of the manufactured and natural worlds.

While field workers stage on the Old 17th Avenue pedestrian bridge over the South Platte River in downtown Denver, bikers, runners, dog-walkers and assorted passers by on a brilliant spring morning slow and stare. They see one team member lean into a pump to inflate a small kayak. Others unpack and stretch a 20-foot-long cone of nylon netting, calibrate instruments and slip into chest-high waders.

One onlooker approaches Mozrall and asks if she’s looking to catch fish. But the team from the Colorado School of Mines is angling to capture another pervasive resident of the waterway: microplastics. 

Mozrall, a 28-year-old doctoral candidate whose dissertation gave rise to this project, lays the groundwork for a solution to the infiltration of microplastics — defined as particles less than 5 mm long — into virtually every aspect of our lives, from fishing streams to bloodstreams. Working with both undergraduates and master’s students, she explores segments of the urban South Platte to determine the amount and types of microplastics that end up in the waterway.

Afterward, lab analysis of the day’s catch will yield further clues to the origin of the material. And overall, the students establish a workflow within the team for future research that extends beyond rivers to oceans and beaches, drinking water and even soil samples.

Although awareness of microplastics as a potential health concern has grown, Mozrall notes that there are still lots of gaps in understanding where they come from and the effects they have on the environment. Her research seeks to quantify some basic questions: How many microplastics end up in the river? What kinds? How big are they? And secondarily, where do they come from?

“There’s still a huge need for primary data, and we can’t model these plastics,” she says. “We can’t establish risk or impacts from microplastics without really understanding where they are, how they move and what’s going on with them. We’re also striving toward understanding them at large better and how they interact with our urban river systems.”

Through connections with Instituto Tecnológico de Santo Domingo, a private university in the Dominican Republic known as INTEC, Mozrall and her Mines colleagues forged a collaboration.  Researchers at both schools have expanded their work to include the Ozama River — a somewhat larger (and more polluted) urban waterway in an area with a similar population density to Denver. 

Mozrall pitched a study that would add a microplastics element to the research, she says, in order to figure out whether microplastics are appearing in similar concentrations and with similar polymer types to the macroplastics that have been observed — or whether they’re functioning in a totally different system.

“There is a very small number of studies that have been done in the Caribbean on microplastics, and nearly no microplastic research in the Dominican Republic,” she says. “And so our research there is really, really ground zero. I think the study we’re hoping to put out would probably be one of the first microplastic studies in the DR.”

Among other findings, the comparison of the two rivers could help determine whether the level of waste management — advanced in Denver compared to the Dominican Republic — could be a factor in the presence of microplastics.

As part of the exchange with Mines, Laura Aquino, a 23-year-old lab technician from INTEC, has joined students from the Golden school to gather data in Denver. Crouching by the bridge railing, she calibrates a flow meter that will measure the rate that the South Platte’s current passes through the net they will use to collect microplastic samples.

She has already seen characteristics that set the rivers in the two countries apart.

“The river water, the looks of it, the parameters that we’re measuring, they’re very different,” Aquino says. “The DR river is more polluted than the Denver rivers. The microplastic content, it’s actually very different between them. We’re still in the preliminary parts of the experiments, but there’s very much a difference.” 

Sampling the South Platte

Before the researchers cast their net for samples, they carry the now fully formed kayak to the river’s edge and launch it into the middle of the lazy current. With a pipe-shaped pumping device, one of the students paddles to different locations and takes water samples from close to the surface and then the subsurface. Plastics have different densities — some float, some sink and some are suspended in between.

Finally, students lower the tubular net into the river by two ropes from atop the bridge. The calibrated flow meter sits centered at the mouth of the tube, spinning with the passage of water. 

The net, whose mesh openings are a tiny 335 micrometers (barely more than 1/100th of an inch), remains submerged for five minutes before the researchers begin pulling it back up to the bridge. By changing out bags with even smaller mesh (between 125 and 250 micrometers) inside the net, the researchers can collect multiple samples without thoroughly cleaning the primary net in between. 

Based on the amount of plastic collected, they’ll have usable data — basically, particles per unit of water — produced by an equation that takes into account the time, flow rate and diameter of the net. 

From there, Mozrall explains, the researchers can return to the lab and process the day’s samples to determine how much of which types of plastics fall in various ranges of size, shape and type.

“Just seeing the volume of plastic that we capture is really alarming sometimes,” she says. “And just shocking.”

Ginger Juzefyk, a 21-year-old senior at Mines who works on the microplastics research team, grew up on the water in New Jersey — Barnegat Bay, which has suffered over the years from pollution carried by rivers that feed it. So the presence of microplastics is, for her, kind of personal.

“Once we have those numbers, once we have those statistics,” she says, “I think it could be really eye opening for people. Just being able to look at a sample of river water and be like, ‘Wow, you can visibly see microplastics in that’ is just a good educational tool.”

Just three days earlier, the project team had done a similar sample collection a few miles upstream, near Chatfield Reservoir, and has plans to do others in the coming days at various locations within the city limits. But here, in the shadow of Empower Field at Mile High, the students work by a storm drain where water — likely the last of the runoff from a spring snowstorm — trickles across the concrete past an empty plastic milk jug and other containers. It’s yet another possible source for microplastics that end up in the river.

Elsa Scherzinger, a 22-year-old master’s student at Mines, met Mozrall in the research lab at the chemistry department when she was still an undergraduate. Although her master’s is focused on environmental modeling, her love of the “water space” made the river-centered microplastics project a natural fit.

“Microplastics are everywhere,” Scherzinger says. “We hear about it all the time, right? ‘Don’t eat on Teflon because microplastics are there.’ But I think protecting our waterways is really important. And I think studying microplastics and seeing where they are is the basis of what we can do. Because once you know where it is, then we can start to make strategies for how to deal with microplastics from there.”

In the lab, the process of analyzing the polymers can be time consuming, but Mozrall hopes to have usable data by some point this summer. The results will probably appear in the form of a peer reviewed publication for further input from the scientific community. 

“I also would love to see how we can get the city involved with some of the data that we’re finding,” Mozrall says, “and see if there’s anything that we can do from more of a legislative standpoint to try to deter these plastics from entering the river in the first place.”

The early analysis of the Denver samples has revealed a lot of tire wear particles — bits of rubber from bike or car tires that eventually find their way into the river via storm drain runoff like the trickle that empties into the South Platte where the researchers sift through its flow.

Mozrall also has noticed a lot of polyethylene, the ubiquitous polymer that’s part of … almost everything, from bags to consumer packaging and lots in between. Its overwhelming presence from such a variety of sources makes it inherently difficult to track. Plus, it’s difficult to determine at what phase it entered the river.

“There could be some pieces that sat in farm soil for 10 years and then a big rain came along and finally washed it into the river,” she says. “Or we could have a particle that just fell off someone’s bike tire five minutes ago — and that could all be in the same sample.” 

By imaging and scanning the particles, the researchers can look for telltale signs like biofilm accumulation or weathering that might offer clues to their origin. But even those can be a mystery. Weathering, for instance, could point toward a particle being in the river for a decade, or just as easily becoming worn from a bumpy trip along river rocks on the journey to Denver from Chatfield Reservoir.

The research team eventually packs up and moves downstream a short distance to City of Cuernavaca Park to take additional samples — there’s a bigger haul here, possibly because the nearby confluence with Cherry Creek bolsters the South Platte’s flow — before the focus shifts back to the lab on Mines’ Golden campus.

The first step involves separating the water from the samples themselves, then adding a “digestion” solution that chemically eats away at the organic material, followed by a density separation that employs another type of solution in which sediments sink, but the plastics float.

Once separated, the plastics get a good rinse with purified, laboratory-grade water. Finally, they’re ready to be scanned, analyzed and become part of the record.

But beyond the data itself, Mozrall has a more general, overarching goal — to make the information available and understandable to people who may not have a science background. 

“Microplastics are such a buzzword right now, and they’re really scary to a lot of people,” she says. “I think understanding more of the science helps to be able to digest it and know what is going on and what you can do to control your own exposure.”

Lake Powell, one of the Colorado River’s most important reservoirs, is set to receive 13% of its normal spring runoff, the lowest amount from upstream snowmelt on record, according to a federal forecast Thursday.

The reservoir, located on the Utah-Arizona border, helps pace the flow of water to millions of people, multibillion-dollar industries, hydropower facilities and protected environments in the immense Colorado River Basin. It is also in dire straits: As of Thursday, it held 23% of its capacity. It’s months away from extremely low water levels that would halt hydropower generation at Glen Canyon Dam. 

The expected record-low inflows won’t help. 

If the forecast is accurate, “it would be the lowest April through July volume on record for Lake Powell,” Cody Moser, a forecaster with the Colorado Basin River Forecast Center, said during a webinar Thursday.

The federal Colorado Basin River Forecast Center tracks conditions in the basin and prepares forecasts used by the federal government to determine how the water for 40 million people in the West should be managed.

Since Oct. 1, about 408,000 acre-feet of water has reached the reservoir. That includes water from the sudden snowmelt triggered by a record-breaking heat wave in March, Moser said.

The expected flow of water into the reservoir this year is about 800,000 acre-feet. There’s still a 50% chance that it could be higher, but the forecasts become more certain with every day that passes, he said.

One acre-foot equals about 326,000 gallons, or the annual water use of two to four urban households.

The basin has just endured one of its worst winters on record. Snowpack was low, temperatures were high and spring precipitation hasn’t been enough to make up for the water deficits. 

It is also in the midst of twin crises: historically low water storage and stalled negotiations over how to manage the basin’s vital water supply. 

The massive reservoir was designed to hold about 24 million acre-feet. Its storage as of Thursday is a mere fraction of that total, 5.6 million acre-feet, according to data from the federal Bureau of Reclamation, which manages Glen Canyon Dam. 

For comparison, Colorado uses about 5.34 million acre-feet of water on average each year, according to the Colorado Water Conservation Board. 

The state used an average of 2 million acre-feet of water from the Colorado River Basin between 2021 and 2025, according to data from the bureau. The Western Slope is within the basin’s boundaries, but Colorado River water is transported through tunnels, pipes and canals to almost every corner of the state.

Lake Powell has fallen to historically low levels over the past 20 years in part because of rising temperatures, changing climatic conditions and unyielding human demands. 

The lake was just 394 feet deep at the dam as of early May. If the water falls too low, it would be unable to pass through the dam to generate hydropower, a reliable, affordable energy source for communities across the West.

The Bureau of Reclamation projections show hydropower generation could stop as soon as September without intervention. Water managers have started holding back water in Lake Powell and releasing water from upstream reservoirs, like Flaming Gorge on the Wyoming-Utah border, to protect the dam’s infrastructure and continue generating power.

An expiring set of reservoir management rules also contributed to the West’s water storage crisis. The rules, established in 2007, allowed the reservoir to be drained even in dire drought years, and officials’ efforts to respond failed to restore the reservoir’s storage. 

Those rules expire this year, and negotiations to replace them have been largely stagnant for months. The new set of rules must be in place by Oct. 1.

During the webinar Thursday, Moser paused and took a breath. 

“Really no good news this winter.”

Colorado has expanded its air pollution-fighting arsenal to an entirely new theater after years of preparation, taking on so-called air toxics like benzene, formaldehyde and hydrogen sulfide from asphalt makers with mandatory control measures meant to protect surrounding low-income neighborhoods. 

State health officials can now monitor emissions and require new equipment and processes for five designated chemicals known to cause higher rates of cancer and other disease. The initial list includes benzene from refineries, ethylene oxide from sterilizers, hydrogen sulfide from asphalt and manure operations, formaldehyde from turbines and combustion engines, and hexavalent chromium from chrome-plating industries. 

Cutting back air toxics adds to Colorado’s other major ongoing air pollution battles: trimming greenhouse gas emissions that contribute to climate change, and capping “criteria” pollutants that permeate the environment at larger scale such as ozone, nitrogen oxide, PM2.5 and volatile organic compounds. Health and environment advocates believe they can make community health progress in minority and low-income neighborhoods disproportionately impacted by industries, through tighter control of a few toxic chemicals from a handful of sites. 

The Air Quality Control Commission earlier this month passed the final rules launching the Air Pollution Control Division into a new regulatory regime for the five chosen chemical emissions. 

“For years, communities living near highways, oil and gas sites and industrial facilities have been exposed to the highest levels of these pollutants — and currently, Colorado does not have strong rules on how much of these chemicals can be in the air,” said Conservation Colorado, after the AQCC vote. “These impacts fall disproportionately on communities of color. Latino people are nearly three times more likely than white people to live in areas with the most harmful air, and Black and Latino communities are more likely to face the worst pollution overall, according to the American Lung Association. This action moves the state closer to changing that.”

Air division director Michael Ogletree said in an interview that issuing the rules directed in a 2022 legislative bill is “really a monumental step in finalizing what we’ve been working on for the past several years, to actually put protections in place for disproportionately impacted communities, as well as Coloradans as a whole, in protections against air toxics.”

Advocates who sought the toxics rules for years say they will watch to see how tightly Colorado enforces the rules, but they welcomed the final steps. 

“This is a meaningful step forward for public health in Colorado. By adopting standards to reduce exposure to the most harmful air toxics, we are moving closer to a future where fewer families are dealing with preventable illnesses linked to pollution. There is still more work ahead, but this action reflects real progress toward protecting the health of our communities,” said Dr. Maria Chansky of Glenwood Springs, family physician and advocate for the nonprofit Healthy Air and Water Colorado.

The 2022 law set in motion a long process at the health department and the commission. The law required the health department to carefully study dozens of toxic chemicals and determine the five that were most hazardous to Colorado’s vulnerable neighborhoods and could also be effectively monitored and controlled. The air division had to pick locations and set up sensitive monitoring devices. 

The toxic substances, causing cancers and many other serious health issues, that were first designated by the new rules include: 

• Benzene — This petroleum byproduct is a major issue at Suncor in Commerce City, Colorado’s only oil refinery. Neighbors in Adams County and north Denver have been subject to multiple industrial emissions and contaminations over the decades, from refinery pollution to highway exhaust to metal smelting residue. To meet the new benzene limits, Suncor will have to add “maintenance activities that maybe need to be done a little bit more frequently,” said Stefanie Shoup, manager of innovations in planning and air quality data for the health department. “We’re adding in this component of looking for benzene emissions, and increasing the frequency of some of those inspections so that they’re being caught and fixed on an earlier cadence.”

• Formaldehyde — It can be produced through multiple industrial processes and manufacturing, but Colorado will focus on larger sources from combustion turbines and other stationary engines. “It’s primarily from engines and turbines, but it’s also a complicated pollutant, because it also is generated just in the atmosphere, through normal breakdown of other types of components in the air,” Shoup said. The new rules require testing, monitoring and installation of new controls at some sources. 

• Hydrogen sulfide — Sources of the toxic emissions include asphalt plants, makers of asphalt roofing tiles, and manure digesters. State health will require industrial sources to employ emission control devices to destroy the gases. Manure digesters will add substances to storage pits that reduce hydrogen sulfide production. 

• Ethylene oxide — A highly toxic chemical primarily used by medical equipment manufacturers to sterilize life-saving gear before shipment. Recent federal rule tightening has already put Colorado’s ETO users on the path to better compliance, state officials said, and the large manufacturer Terumo in Lakewood has been installing control equipment that it says were ahead of new requirements. 

• Hexavalent chromium — Yes, it’s the infamously dangerous substance at the heart of the toxic detective work in the 2000 film “Erin Brockovich,” but Colorado’s emissions come mostly from chrome-plating businesses. State officials said the sources “can improve work practices to reduce emissions, conduct additional testing, or switch to less toxic and volatile forms of chromium.”

The air commission can revisit and may add to the list of controlled toxic substances every five years, and the air pollution division staff said they are eager to continue rounding out a new area of health regulation. 

“What we heard very loud and clear is that communities are interested in expanding these requirements wherever we can, and we’re very interested in doing the same,” Shoup said. “While we’ve had four years now, this is also the type of program that can take a decade or more to truly build out to the kind of program that we would like to see. We spent 30 or 40 years building the criteria air pollutant program. And so here we are. I think there’s a lot of good that we can do in the future.”

More than half of “long-shot” bets on military action made on Polymarket are successful, according to a new report that suggests prediction markets could pose a bigger threat than previously recognized to the security of sensitive information.

Analysis by the Anti-Corruption Data Collective, a non-profit research and advocacy group, found that long-shot bets—defined as wagers of $2,500 or more at odds of 35 percent or less—on the platform had an average win rate of around 52 percent in markets on military and defense actions.

That compares with a win rate of 25 percent across all politics-focused markets and just 14 percent for all markets on the platform as a whole.

The research is likely to add to growing concerns among regulators and lawmakers about insiders placing bets on the timing and success of military actions, amid fears that this could reveal classified information in advance.

The report, which analyzed more than 400,000 prediction markets settled on Polymarket between January 2021 and March 2026, comes as US prosecutors last week charged a soldier involved in planning the January raid to seize Venezuelan leader Nicolás Maduro with placing Polymarket wagers on the mission that netted more than $400,000.

Gannon Ken Van Dyke, an active duty soldier, is alleged to have made roughly 13 bets worth $33,034 on positions including “US Forces in Venezuela” and “Maduro out” while in possession of classified information. On Tuesday Van Dyke pleaded not guilty.

The charges represent the first US prosecution of insider trading on prediction markets. Earlier this year Israel filed charges against a reservist and a civilian accused of using classified information to bet on the country’s military operations on Polymarket.

Political markets where outcomes can be determined by small decision-making groups, particularly military and defense markets, are “structurally vulnerable to insider trading,” said the ACDC, adding that the dynamic not only threatens information security but also “disadvantages regular bettors.”

Credit: Financial Times

Yassamin Ansari, a Democratic lawmaker from Arizona, has called wagers on military actions “a disturbing national security risk,” while Ritchie Torres, a Democratic representative from New York, has said markets on political and military decisions risk creating “a perverse incentive” for government insiders “to personally push policies that line [their] pockets.”

The report also found that markets on cultural events, such as competition winners or music releases, were disproportionately likely to host suspicious wagers, with 29 percent of long-shot bets in these markets proving successful.

The Nobel Peace Prize organizers investigated a potential leak last year after online betting surged in favour of Venezuelan opposition leader María Corina Machado just hours before she was announced as the winner.

There have also been concerns about market manipulation. France’s weather forecasting service this month filed a police complaint after detecting anomalies in its temperature gauges in Paris, which coincided with a surge in well-timed bets on Polymarket.

Some of Polymarket’s military and political markets have attracted heavy betting. Markets on whether the US and Iran will reach a permanent peace deal have seen $63 million in trading volume, while one on whether China will invade Taiwan in 2026 attracted $23 million. But sports wagers continue to dominate the platform, with trading volume on which team would become the Super Bowl champion earlier this year exceeding $700 million.

Polymarket declined to comment on the report. The company has previously said it prohibits trading on stolen confidential information or by those who can influence the outcome.

In a post on X last week, Polymarket said Van Dyke’s arrest was “proof the system works.” The company said that when it identified “a user trading on classified government information,” it referred the matter to the US Department of Justice and cooperated with their investigation.

Amid increased scrutiny over suspected insider trading, prediction market platforms have tried to reassure customers and lawmakers that they are cracking down on market manipulation.

Kalshi, Polymarket’s major rival, has heavily promoted its own efforts, including a partnership with market surveillance company Solidus Labs, as it seeks to distance itself from Polymarket and emphasize its credentials as the largest regulated platform in the US.

Kalshi bans what it calls “violent markets, including war and kidnapping”—although it does allow markets on the closure of the Strait of Hormuz—saying that markets should “not incentivize harm,” while it also requires proof of identity. In contrast, Polymarket does not require most users of its international site to provide proof of identity and allows payment using anonymous cryptocurrency channels.

Growing scrutiny has created a business opportunity for a wave of start-ups selling tools to help users profit by copying suspected “insiders.”

“The platforms are creating new rules to try to root them out and make it clear they don’t allow that activity. That to me [ . . . ] proves there is some informed flow in these markets worth following,” said Matt Saincome, chief executive of financial data provider Unusual Whales, which sells a $20-a-month “unusual predictions” tool to monitor suspicious bets on Polymarket.

Another start-up, Polywhaler, promises to help traders “monitor large bets in real-time” for $4.99 a month.

Polymarket has itself published a list of the 10 most-copied wallets in a blog post, including recommendations for traders on strategies to follow and pitfalls to avoid when copy-trading.

The company and Kalshi have long argued their platforms harness collective wisdom to accurately forecast events. But another recent study has found prediction markets reflect the “wisdom of an informed minority” rather than the “wisdom of crowds.”

Only 3 percent of all accounts generate the bulk of price discovery, according to a study led by Roberto Gómez Cram, assistant professor of finance at the London School of Economics.

These are traders whose accounts predict prices and react quickly to breaking news, making outcomes more accurate for markets on Polymarket, the platform studied by the researchers.

The rest do not “produce wisdom,” the study said, and therefore are more likely to lose money. Instead, they fund skilled traders by generating most of the volume, “but little of the information, and their losses flow as profits to the informed minority.”

© 2026 The Financial Times Ltd. All rights reserved. Not to be redistributed, copied, or modified in any way.

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