Polymarket and Kalshi open betting markets on measles and US health policy

A sign pasted on a construction fence beside an elementary school in Brooklyn looked, at first glance, like a routine public health message: bold capital letters reading 'Vaccines' on a star-spangled blue background. Smaller text at the bottom asked, 'Will any state end vaccine markets?' — next to the logo of Polymarket, the online prediction market. The platform is now taking wagers on public health, joining Kalshi, which started listing health-related predictions over the summer.

The contracts on offer cover a lot of medical ground. Users can bet on when the US Food and Drug Administration will approve a skin-cancer vaccine, or whether the Centers for Disease Control and Prevention will change its vaccine recommendations. They can wager on drug trial outcomes and approvals, on how many measles cases the US might see in 2026, and on whether the country loses its measles-elimination status this year.

Prediction markets are largely unregulated, even though they are functionally 'identical' to regulated gambling, said Lia Nower, a professor and director of the Center for Gambling Studies at Rutgers University. The companies position themselves as financial derivatives rather than traditional bets — a regulatory loophole that puts them under federal commodities law and the oversight of the Commodity Futures Trading Commission, not state gambling regulators. Several states have sued the companies alleging they operate as gambling sites. 'Gambling right now is like the wild, wild west,' Nower said.

Critics see a direct route from wagers to policy. Advocates, officials and lawmakers could bet on ending state vaccine mandates and then introduce laws to do it, Nower said, and there appear to be no laws against that. Bets also exist on when certain officials will leave health agencies, which resignations or firings could settle. Matthew Eisenberg, professor and chair of health policy and management at the Johns Hopkins Bloomberg School of Public Health, said FDA and trial contracts 'create a payoff for anyone with nonpublic information,' and warned that the real exposure is leaks. 'The risk isn't necessarily that a reviewer takes a bribe — it's that the market now rewards leaks,' he said.

Polymarket did not answer the Guardian's questions about the consequences for public health or medicine. Kalshi did not respond on the record, but spokesperson Dani Lever argued the trial and approval markets improve transparency, calling them 'a pilot program aimed at a structural problem in drug development: the people who best know whether a trial will succeed are scattered, and their insight rarely reaches the public.'

Problem gambling is itself a fast-growing public health concern, Nower said, hitting younger, Black, Hispanic and lower-income people hardest. A new report she co-authored found more than half of people aged 13 to 27 gambled in the past year; among those young gamblers, 39.5% carried some degree of gambling-related risk and 10.3% were high risk. Eisenberg's own research on online sports betting linked legalization to measurable rises in treatment for depression and anxiety among young men — and prediction markets sit outside the state-level protections, like deposit limits, self-exclusion rules and treatment funding, that followed. 'In effect, these are gambling products that have exited the only regulatory system designed to limit gambling harm,' he said. New Jersey is among the states moving to restrict the markets, with consumer protection and insider trading among the concerns. Eisenberg cautioned against reading the health contracts as public opinion, noting that prices that small can be moved by a single trader: 'A few-hundred-dollar contract on the childhood vaccine schedule is not a forecast of anything.' Within a week, the Brooklyn sign was vandalized — the bottom half, logo and all, torn away, leaving only the word 'Vaccines.'