Hantavirus pandemic odds: Polymarket gives about 1% after $19 million of trading, down from a 10% peak in May
Will hantavirus become a pandemic in 2026? Polymarket’s market, which needs the WHO to call it a pandemic, trades at about 1.25% after $19 million of bets, down from almost 10% when the MV Hondius cruise-ship outbreak was in the news in May. Kalshi prices a WHO emergency declaration at under 3%. What happened, what the markets need to pay out, and what has already been settled.
In this article
The prediction markets see almost no chance that hantavirus becomes a pandemic this year. Polymarket’s market “Hantavirus pandemic in 2026?” trades at 1.25%, with a bid of 1.2¢ and an ask of 1.3¢. More than $19 million has changed hands on it since it opened on 4 May, making it one of the most traded health questions on any prediction market.
The price peaked at almost 10% in early May, when an outbreak of Andes virus on the cruise ship MV Hondius spread across several countries. It has fallen almost steadily since. The World Health Organization considers that outbreak over: no new cases were reported after 25 May, and the last quarantined contact went home on 2 July, according to the UK’s travel health service. Kalshi’s market on whether the WHO declares hantavirus a public health emergency of international concern this year trades at 2.8¢.
The odds
Source: Polymarket and Kalshi public market data
- Polymarket, pandemic in 2026: 1.25%, with $19,060,862 traded and about $121,000 in the last day.
- Kalshi, WHO emergency (PHEIC) in 2026: last trade 2.8¢, with a bid of 0.8¢ and an ask of 2.2¢, and about 2.04 million contracts traded since it opened on 7 May.
- Polymarket, any new pandemic in 2026: 2.05%, $1.31 million traded.
- Polymarket, hantavirus vaccine approved by the FDA in 2026: 3.2%, $143,000 traded.
What has to happen for “Yes”
The Polymarket market resolves Yes only if the World Health Organization explicitly calls hantavirus, hantavirus pulmonary syndrome, haemorrhagic fever with renal syndrome or a hantavirus outbreak a “pandemic” in an official public communication by 31 December 2026, 11:59 p.m. ET. Official statements, reports, briefings and publications count if they clearly describe the outbreak as a pandemic.
The rule adds a line that matters: a Public Health Emergency of International Concern alone does not count unless the WHO also calls it a pandemic. A PHEIC is the WHO’s highest alarm under the International Health Regulations, and it is what Kalshi’s market asks about. So Kalshi’s 2.8¢ is a price on a lower bar than Polymarket’s 1.25%, and it is consistent for it to be higher.
With about seven weeks left, the market needs a new outbreak large enough, and fast enough, for the WHO to use the word. Nothing in the official record since the summer points that way.
What happened in 2026
Source: Polymarket price history (daily)
Show the dataHide the data
| Yes | |
|---|---|
| 5 May | 4.95% |
| 8 May | 9.85% |
| 20 May | 6.25% |
| 1 Jun | 5.45% |
| 12 Jun | 3.65% |
| 5 Jul | 2.35% |
| 11 Aug | 3.65% |
| 15 Sep | 2.55% |
| 6 Oct | 2.25% |
| 16 Oct | 1.45% |
| 9 Nov | 1.55% |
The MV Hondius outbreak. The expedition ship MV Hondius left Ushuaia, Argentina, on 1 April 2026 and sailed across the South Atlantic, according to a WHO notice summarised by the UK’s National Travel Health Network and Centre (TravelHealthPro). The virus was confirmed as Andes hantavirus, a strain found in South America.
More than two dozen passengers left the ship at St Helena on 24 April and dispersed to about a dozen countries, including Turkey, Singapore, New Zealand and the United States, NPR reported on 7 May. The first patient had been bird-watching at a landfill outside Ushuaia with his wife before the cruise, according to Dr. Jeanne Marrazzo of the Infectious Diseases Society of America, though that exposure had not been confirmed. He boarded without symptoms, fell ill a few days into the voyage, and the virus spread to others, including his wife. Both died, as did a German woman on board.
The case count grew through May:
- 7 May: 8 cases, 5 confirmed, 3 deaths (WHO, via TravelHealthPro).
- 18 May: 11 cases, 9 confirmed and 2 probable, 3 deaths. Confirmed cases were being treated and isolated in France, the Netherlands, South Africa, Switzerland and the United States.
- Final: 13 cases, 12 confirmed and 1 probable, including 3 deaths. No cases were reported after 25 May.
On 3 July TravelHealthPro reported that the final contact had completed quarantine, tested negative and returned home on 2 July, and that the WHO considers the outbreak over.
Why it caused alarm. Andes virus is the only hantavirus known to spread from person to person, NPR reported, citing infectious-disease specialist Dr. Emily Abdoler. Most hantaviruses reach people through rodents. WHO Director-General Tedros Adhanom Ghebreyesus said transmission between people “has been associated with close and prolonged contact, particularly among household members, intimate partners and people providing medical care.” The CDC puts the death rate of hantavirus infection at 30% to 40%, though Marrazzo said that is probably an overestimate because mild cases go uncounted.
Why the WHO pushed back. At a briefing in early May, the WHO’s Maria Van Kerkhove said: “I want to be unequivocal here. This is not the start of a COVID pandemic.” She added: “This is not COVID. This is not influenza. It spreads very, very differently.” The WHO described the risk to the global population as low.
The market followed the official tone. From 9.85% on 8 May it fell to about 6% by late May, below 4% in mid-June and around 2% to 4% through the summer. It dipped to 1.45% in mid-October and has mostly stayed between about 1.2% and 1.7% since, apart from a brief spike to 5.2% on the evening of 29 October that faded over the following day.
The markets that have already settled
Source: Polymarket public market data
Show the dataHide the data
| Value | |
|---|---|
| US case confirmed by 15 May: Yes | $1.30m |
| Lab leak confirmed by 30 June: No | $0.68m |
| WHO emergency by 30 June: No | $0.09m |
| US case confirmed by 31 May: Yes | $0.03m |
The cruise-ship outbreak spawned a cluster of short-term markets, and their results say a lot about how the story played out:
- “Confirmed case of hantavirus in the US by 15 May?” settled Yes, after $1.30 million of trading. The rules counted any laboratory-confirmed hantavirus infection identified in US territory, wherever the person was exposed. The price was 26¢ on 8 May and 46.5¢ on 10 May before the market settled. A follow-up on a further US case by 31 May also settled Yes.
- “Hantavirus lab leak confirmed by 30 June?” settled No after $684,000 of trading; it opened under 3¢.
- “Hantavirus outbreak by 30 June?”, which asked whether the WHO would declare a PHEIC by that date, settled No. It opened at 22.5¢ on 12 May and fell quickly.
So the pattern was the same throughout: cases did spread to several countries, including the US, but the official escalations that the bigger markets needed never came.
Kalshi v Polymarket
The two exchanges ask different questions, so their prices are not directly comparable, but they tell the same story.
- Kalshi asks whether the WHO declares hantavirus a PHEIC in 2026. Its last trade was 2.8¢, but the live quotes are a bid of 0.8¢ and an ask of 2.2¢, a midpoint of about 1.5¢. With about 2.04 million contracts traded, it has been one of Kalshi’s busier science markets.
- Polymarket asks for the stronger outcome, the word “pandemic”, and prices it at 1.25%.
At the midpoints the two are close: about 1.5¢ for an emergency declaration on Kalshi and 1.25¢ for the word “pandemic” on Polymarket. Both markets are saying that the WHO is very unlikely to escalate hantavirus before the end of the year, and neither has seen a lasting rise since the summer. If a new cluster appeared, you would expect Kalshi’s emergency market to move first, because a declaration of that kind can come earlier in an outbreak than talk of a pandemic.
Hantavirus is still out there
None of this means hantavirus has gone away. It is endemic in parts of South America and elsewhere. In Argentina, the Buenos Aires provincial health ministry reported 18 confirmed cases and 7 deaths in 2026 by the week of 3 to 9 May, a 50% rise on the same period of 2025, the Buenos Aires Herald reported; the province recorded 37 cases and 12 deaths in all of 2025.
Endemic cases like these, mostly caught from rodents in rural areas, are not the kind of fast human-to-human spread that would lead the WHO to talk about a pandemic. They are a reminder that new clusters can appear, but they are not what the market needs.
Related markets
- Any new pandemic in 2026 (Polymarket): 2.05%. This pays if the WHO declares any disease a pandemic this year, so it should be at least as high as the hantavirus market, and it is.
- Ebola pandemic in 2026 (Polymarket): 1.45%, $816,000 traded.
- Hantavirus vaccine in 2026 (Polymarket): 3.2%. This needs full FDA approval of a human hantavirus vaccine by 31 December. NPR reported in May that there is no vaccine or specific treatment for hantavirus.
How to read a 1% price
A price of 1.25% means traders put the chance at about one in eighty. Buying Yes at 1.3¢ pays $1 if it happens, about 77 times the stake. Buying No at about 98.8¢ pays $1 if nothing happens by 31 December, a return of about 1.2% in seven weeks.
Neither is free money. Long-shot markets often trade a little above their true chance, because a small stake can win a lot (are prediction markets accurate?). On the other side, selling at 98.8¢ ties up capital for a small gain, and the fee matters: Polymarket charges takers 5% × price × (1 − price) on this market, which is small at these prices but not zero (Polymarket fees). For how to judge whether a price is good value, see how to calculate expected value.
What would move the price
- A new cluster with person-to-person spread, especially outside South America, would move both markets quickly.
- WHO statements. The market turns on the WHO’s exact words. Any briefing that discusses pandemic risk will move it, and the rules require the word itself, not a hint.
- The calendar. Every week without news makes Yes less likely. The market expires at the end of 2026.
FAQ
Is there a hantavirus pandemic? No. The WHO has not called hantavirus a pandemic, and it considers the 2026 cruise-ship outbreak over.
What are the odds of a hantavirus pandemic in 2026? About 1.25% on Polymarket as of 9 November 2026.
Did the WHO declare a public health emergency? Not as of 9 November 2026. Polymarket’s market on a declaration by 30 June settled No, and Kalshi prices one by the end of 2026 at under 3¢.
Were there hantavirus cases in the US? Polymarket’s market on a confirmed case in US territory by 15 May settled Yes under rules that counted any confirmed infection identified in the US.
Live prices: hantavirus pandemic on Polymarket, WHO emergency on Kalshi and any new pandemic.
Prices as of 9 November 2026. Sources: Polymarket and Kalshi market data; TravelHealthPro (UK National Travel Health Network and Centre) updates of 7 May, 20 May and 3 July 2026; NPR’s outbreak update of 7 May 2026; the Buenos Aires Herald. Nothing here is medical or financial advice.
