Why is the Polymarket hantavirus pandemic probability changing?

The 'Hantavirus pandemic in 2026?' market on Polymarket has been one of the most volatile health-related markets of the year. Launched on May 4, 2026, it opened at 3.5%, spiked to 38% on May 5 as initial reports of human-to-human transmission and deaths emerged, then fell back to 9% by May 7 after the WHO Director-General publicly framed the cluster as 'not the next COVID'. Total trading volume has crossed $2.2 million. Movement reflects a real-time crowd assessment of three signals: (1) WHO's risk framing, (2) new case reports outside the original ship cluster, and (3) the 6-week incubation period meaning new cases could still emerge through mid-June 2026. The market resolves on December 31, 2026 — bettors are pricing the entire 8-month tail risk.