Prices and volume as of August 18, 2026, fetched from Kalshi's public market data.
The Quick Answer
The Kalshi hantavirus market asks one question: will the World Health Organization declare hantavirus a Public Health Emergency of International Concern in 2026? The market's answer is about 3 cents. The last trade printed at 3.1 cents on a 2.2-cent bid and a 4.9-cent ask, an implied chance between roughly 2.2% and 4.9%. It traded as high as 98 cents the day it listed in May, when a cruise-ship outbreak in the Atlantic was the scariest health story on the wires. WHO declared that outbreak over on July 2, 2026, and the price has been pinned in the single digits since. The full arc (the outbreak that created this market, the 95-cent collapse, why yesterday's roughly 150,000-contract session was its busiest since the May panic, and what would actually have to happen for YES to cash) is below.
What The Market Is
Kalshi lists the contract as KXNEWOUTBREAKHANTA-26: "Will WHO declare Hantavirus a Public Health Emergency of International Concern this Year?" The resolution rule is one sentence. If hantavirus becomes a Public Health Emergency of International Concern in 2026, the market resolves YES; it settles against WHO's own emergencies page, runs through December 31, 2026, and closes early the morning after a declaration if one ever comes. Like every contract on a prediction market, the price is the probability: a 3-cent contract is the crowd saying roughly 3%.
Two numbers frame how seriously traders have taken the question. Lifetime volume stands at about 1.82 million contracts, and open interest (positions still held open) sits near 491,000. That is real, sustained participation for a market about a rodent-borne virus most people had never thought about before this spring. The reason they thought about it is a ship.
The Outbreak That Created This Market
On May 2, 2026, WHO was notified of a suspected hantavirus outbreak aboard the M/V Hondius, a cruise ship that had left Ushuaia, Argentina on April 1 and was moored off Cabo Verde by early May. The pathogen was Andes virus, the only hantavirus known to spread from person to person, and the early bulletins were grim. WHO's first outbreak report on May 4 counted seven cases and three deaths, with illness onsets stretching back to April 6. By late May the count had grown to 13 cases across passengers and crew from multiple countries, and WHO's follow-up reporting confirmed the part that made this different from every prior hantavirus story: limited human-to-human transmission had occurred on board, and more than 600 contacts across 32 countries, territories, and areas were being monitored through 42-day follow-up windows.
Kalshi listed this market on May 7, five days into that news cycle, and the opening session tells you exactly what the moment felt like: the contract opened at 90 cents, printed as high as 98, and closed its first day at 39. For a few hours, traders priced a formal WHO emergency declaration as a near-certainty. It never came. Here is what the market did instead.
| Date | Close | Implied probability | Session context |
|---|---|---|---|
| May 7, 2026 | 39¢ | 39% | Listing day; opened at 90¢, touched 98¢ |
| May 8, 2026 | 20.9¢ | 21% | First full session; ~106,500 contracts traded |
| May 13, 2026 | 17.9¢ | 18% | Heaviest session in market history, ~170,800 contracts |
| May 19, 2026 | 8.3¢ | 8% | First single-digit close |
| May 24, 2026 | 12.1¢ | 12% | Brief rebound; last double-digit closes May 24-25 |
| June 1, 2026 | 6¢ | 6% | Case count static at 13; no new cases reported |
| July 2, 2026 | 2.1¢ | 2% | WHO declares the outbreak over |
| August 18, 2026 | 3.1¢ last trade | 2.2% to 4.9% by the live quote | Bid 2.2¢ / ask 4.9¢ |
The row I keep coming back to is May 19. That first single-digit close came less than two weeks after the 98-cent print. The decay wasn't perfectly smooth — the price popped back to 12.1 cents on May 24 and 11.7 on May 25, a last flare of worry while hundreds of contacts were still inside their monitoring windows — but those were the market's final double-digit closes, and no daily close since has been higher than the 8.4 cents it settled at on May 27. Prices are the crowd's live read on new information, and the information kept pointing one way: the case count stopped at 13 (with 3 deaths), the 600 monitored contacts did not turn into new chains of transmission, and the patients had been evacuated at Tenerife and the ship docked in Rotterdam by May 18. When WHO officially declared the outbreak over on July 2, the market barely moved: the contract closed that day at 2.1 cents, having already spent a month pricing the outcome. Since then it has drifted in a 2-to-7-cent band, which reads as the noise of a thin order book more than any change of view.
What A PHEIC Actually Takes
So why isn't the price zero? To answer that, you need to know what the contract is actually waiting for, and the bar is high. A Public Health Emergency of International Concern is the loudest alarm in global health law, defined under the International Health Regulations (2005): an extraordinary event that risks spreading disease across borders and may require a coordinated international response. Only the WHO Director-General can declare one. Since the mechanism was created, it has been invoked nine times: H1N1 flu in 2009, polio in 2014, West Africa Ebola in 2014, Zika in 2016, the Kivu Ebola outbreak in 2019, COVID-19 in 2020, mpox in 2022, mpox again in 2024, and, this May, Ebola once more. Hantavirus has never been on that list.
The 2026 entry is the comparison I find most clarifying, because it happened in the middle of this market's own collapse. On May 17, 2026, WHO declared the Bundibugyo Ebola outbreak in DRC and Uganda a PHEIC, the Director-General moving so urgently he issued the declaration before convening his expert committee, a first. That is what a declaration-worthy event looks like: an ongoing, spreading outbreak of a high-fatality filovirus across two countries. Ten days earlier, hantavirus traders had briefly priced their own contained, single-ship outbreak (13 cases at its final count) at similar certainty. The same organization looked at both events in the same month and reached for the alarm exactly once. Kalshi carries a sibling market on Ebola (KXNEWOUTBREAKEBOLA-26), though note the fine print cuts differently there: it asks whether Ebola becomes a pandemic, a higher bar than a PHEIC, which is why that contract trades at just 5 cents even with a live PHEIC on the books.
The bear case in one sentence: the outbreak that created this market ended seven weeks ago, so for YES to cash by December 31 a brand-new hantavirus event would have to emerge and clear a bar that the Hondius outbreak, with confirmed person-to-person spread and contacts in 32 countries, never cleared while it was live.
Reading A 3-Cent Contract: A Worked Example
Penny markets punish sloppy reading, so here is the discipline applied to today's board. The last trade printed at 3.1 cents, but the live quote is 2.2 bid, 4.9 ask. If you wanted to buy YES right now, you'd pay 4.9 cents, an implied probability near 4.9%, not 3.1%. Sell it, and you'd collect 2.2, closer to 2.2%. That 2.7-cent spread is the real cost of doing business, and on a base price this small it is enormous: buy at the ask and the market must more than double just for you to get out flat at the bid. The order book behind those quotes is thin (a handful of contracts on each side at last check), so my honest read of the price is a range, roughly "2% to 5%," not a false-precision single number. This market also ticks in tenths of a cent, which is why prints like 3.1 exist at all. It is the same shop-the-number discipline sports bettors use on a live odds screen: the quoted price you can actually transact at, not the last price something traded at, is the number that counts. The mechanics of placing this kind of trade, tick sizes and order types included, are covered in our guide to how to bet sports on Kalshi, and they work the same on an outbreak contract as on a point spread.
Run the payout math and the market's logic becomes clear. A YES buyer at 4.9 cents is being offered roughly 19-to-1: risk about a nickel to win about 95 cents if a declaration lands by New Year's. The trader on the other side of that print is risking about 95 cents to keep the nickel, a return around 5% tied up for four and a half months, betting that a thing which has never happened doesn't happen. Neither side is obviously wrong, which is precisely what a low-single-digit price means: the market is treating a hantavirus PHEIC in 2026 as a live tail risk, not an impossibility, priced against the historical fact that nine declarations in two decades have gone to other diseases.
What Yesterday's 150,000 Contracts Were Really Doing
Here's the wrinkle that put this market back on my radar this week: in the last 24 hours, roughly 149,900 contracts changed hands, the market's busiest session since the May 13 panic peak of about 170,800, with one crucial difference between the two visible in the plumbing. During that session, open interest fell from about 626,600 contracts to about 491,000. Volume with rising open interest is new money taking new positions; volume with collapsing open interest is old positions being closed out. Yesterday was overwhelmingly the second kind: a mass unwind, with the price whipping between 1.7 and 7 cents as roughly 135,000 contracts' worth of open positions were flattened. The likeliest story is mundane. NO holders who have been sitting on near-max-value positions since June took their nickels off the table, and YES longshots cut losses, months before expiry. It is a reminder that a volume spike on a prediction market is a headline number that tells you nothing by itself; the open-interest line underneath tells you whether money is arriving or leaving. Here, it left.
The Bottom Line
The Kalshi hantavirus market is a completed story still trading on its epilogue. It was born at 90 cents in the scariest week of a real outbreak (Andes virus, a cruise ship, 13 cases, 3 deaths, person-to-person spread, contacts monitored in 32 countries) and it has spent every week since converging toward the base rate, as the case count froze, the outbreak was declared over on July 2, and WHO's one actual emergency declaration of 2026 went to Ebola instead. At a 2.2/4.9 book, the crowd calls a hantavirus PHEIC this year a 2%-to-5% proposition, and yesterday's roughly 150,000-contract session, its busiest since mid-May, was position-closing flow, not a new scare. The May 7 traders who paid 98 cents were answering the question "is this outbreak frightening?" The market's job, then and now, was answering a narrower one: "will the Director-General pull the alarm by December 31?" Those are different questions, and the 95-cent gap between them is the most instructive chart any of Kalshi's outbreak markets has produced. When our AI model panel takes a position on boards like these, every call is publicly graded against settlement on the Model Verdict Scoreboard; the day-to-day read on how the whole Kalshi board trades lives at Kalshi picks today, and the fee math that matters at penny prices is its own read.
FAQ
What is the Kalshi hantavirus market? It is a binary contract, ticker KXNEWOUTBREAKHANTA-26, that resolves YES if the World Health Organization declares hantavirus a Public Health Emergency of International Concern in 2026, and NO otherwise. It settles against WHO's own emergencies page and closes December 31, 2026. As of August 18, 2026, the last trade was 3.1 cents, on a 2.2-cent bid and a 4.9-cent ask.
Why did the hantavirus market spike in May 2026? Kalshi listed the market on May 7, 2026, five days after WHO was notified of an Andes virus outbreak aboard the M/V Hondius cruise ship: 13 cases and 3 deaths, with confirmed limited person-to-person transmission and more than 600 contacts monitored across 32 countries. The contract opened at 90 cents and touched 98 before closing its first day at 39; it fell to single digits by May 19 as the outbreak was contained. WHO declared the outbreak over on July 2, 2026.
Has WHO ever declared hantavirus a public health emergency? No. The PHEIC mechanism, created under the 2005 International Health Regulations, has been invoked nine times, for H1N1, polio, Ebola (three times, most recently the Bundibugyo outbreak declared on May 17, 2026), Zika, COVID-19, and mpox (twice). Never for hantavirus.
What is hantavirus, and does it spread between people? Hantaviruses are rodent-borne viruses that can cause severe, sometimes fatal disease in humans, typically contracted from rodent droppings rather than other people. The exception is Andes virus, found in South America, the only hantavirus with documented person-to-person transmission, which is what made the 2026 cruise-ship cluster alarming enough for WHO to track contacts in 32 countries.
To be explicit: the prices and volumes on this page are live market data presented as informational content, not financial advice, and nothing here recommends any trade. This page makes no predictions about public health outcomes and no recommendations about health precautions; for actual guidance on hantavirus, see WHO and CDC. Kalshi lists CFTC-regulated event contracts for adults 18 and over (18+), and availability varies by state; check the platform's own eligibility rules.
