Measles Cases in the U.S. by May 31: Market Signals

The U.S. measles outbreak has crossed enough thresholds that the prediction market trading on whether confirmed cases reach 1,800 by May 31 is sitting at 99% YES. That is not a close call. The CDC has been tracking a sustained, multi-state outbreak throughout 2026, and the case count trajectory has consistently outpaced earlier projections. The market reached this price after a dramatic single-session move, which means traders repriced the contract to near-certainty based on data that has become very hard to argue with.

As of late April 2026, CDC case count data puts confirmed measles infections well above 1,000 for the year, with the pace of new reports still elevated. The 1,800-case threshold by May 31 now requires roughly 800 additional confirmed cases over the remaining weeks of May. Given current reporting rates, the market has concluded that barrier falls. Here is what the measurements are telling us: the outbreak dynamics, not wishful thinking, are driving this price.

How the 1,800-Case Threshold Contract Works

This contract resolves YES if the CDC confirms at least 1,800 measles cases in the United States by May 31, 2026. Resolution NO requires the confirmed count to remain below 1,800 on that date. The CDC’s official case count, updated weekly on the agency’s measles outbreak tracker, serves as the authoritative source.

• YES (1,800+ cases by May 31): $0.99 | 99% implied probability
• NO (fewer than 1,800 cases by May 31): $0.01 | 1% implied probability

The CDC misses the 1,800 threshold only if case reporting slows dramatically in the final weeks of May. A sudden, sustained drop in transmission rates, combined with a lag in confirmed case reporting, is the only credible path. The agency’s weekly updates have shown no sign of that deceleration. A reporting anomaly or data revision could technically delay official confirmation, but the structural case count trend makes that scenario remote.

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Momentum and Market Signals: A Single-Session Repricing

The momentum composite here is striking. A 24-hour price change of +81.5%, a 1-hour change of +0.9%, and a trend score of 33.67 combine to describe one thing: a market that repriced from genuine uncertainty to near-certainty in a single session. The most probable driver is a CDC weekly update that pushed the confirmed case count into a range where 1,800 by May 31 became arithmetically difficult to avoid.

Total market volume sits at $1,927, with $1,664 of that trading in the last 24 hours. Liquidity stands at $38,679. Volume below $1 million means this market can move sharply on a single data release, and it already did. The thin volume also means the 99% price reflects a small number of trades, not broad market consensus. The data favors the current price, but the liquidity profile means any unexpected CDC revision could create a quick swing.

• 24h price change (+81.5%): The CDC’s most recent weekly case count update almost certainly triggered this repricing, pushing the contract from genuine uncertainty to near-certain YES territory.
• 1h price change (+0.9%): The market is stabilizing at 99% after the large session move, with no new data pushing further in either direction.
• Trend score (33.67): Confirms directional conviction, not noise. The signal is consistent with a data-driven repricing, not speculative positioning.
• Liquidity ($38,679) vs. volume ($1,927): Liquidity vastly exceeds trading volume. The order book can absorb moves, but thin actual trading means price discovery here rests on very few transactions.
• Related market signal: The companion contract tracking total 2026 U.S. measles cases is already at 100%, which is the strongest possible corroborating signal for this contract’s current price.

Lines Analysis: CDC Data Versus the Remaining Calendar

The CDC’s confirmed case trajectory is the clearest signal in this market. Weekly case counts reported through mid-to-late April show the outbreak maintaining active transmission across multiple states. The math is straightforward: if the current weekly reporting rate continues at even a fraction of its recent pace, the 1,800-case total gets crossed before May 31. The companion Polymarket contract on total 2026 U.S. measles cases sitting at 100% is the strongest corroborating data point available.

The single credible NO scenario requires CDC reporting to stall. That could happen if transmission genuinely collapses in the next few weeks and the agency’s lag in confirming cases means the official count does not cross 1,800 before the resolution date. The CDC typically updates its outbreak tracker weekly, so there are only a handful of remaining data points before May 31. A missed weekly update or a sharp revision in methodology could technically delay confirmation, but those scenarios carry very low probability given CDC’s consistent reporting cadence in 2026.

Signals to monitor before May 31:

• CDC’s weekly measles outbreak tracker updates, typically published on Thursdays, will either confirm continued case accrual or signal an unexpected slowdown in transmission.
• Any CDC press release or outbreak summary revising the 2026 case count methodology would directly affect resolution.
• State health department reports from Texas, Ohio, and other high-burden states can serve as leading indicators before CDC national confirmation.
• Vaccination campaign announcements from HHS or state agencies could signal transmission interruption, though the timeline is too short to affect case counts before May 31.
• The companion 2026 annual case count market at 100% provides a directional anchor. If that market moves, this one moves.

Total market volume is $1,927. That thin figure means this market’s 99% price is directionally correct given CDC data, but it is not backed by deep liquidity. The data clearly favors YES. The remaining question is purely about timing and reporting mechanics, not outbreak trajectory.

LINES VERDICT

Confirmed: CDC Case Count Makes 1,800 the Line, Not the Question

The CDC’s 2026 outbreak data has made this contract’s YES outcome the arithmetic default, not a prediction. The outbreak trajectory and the companion annual case market at 100% leave no credible alternative path.

What the market says: 99% implied probability means traders have effectively closed the book on NO. Given the thin $1,927 in total volume and the May 31 resolution date, a surprising CDC revision or reporting delay is the only event that reprices this contract before close.

Key unknown: The CDC’s next weekly case count update is the single most important data point remaining. If it shows continued case accrual at recent rates, this market stays at 99%. An unexpected data revision or a reporting pause is the only variable that matters now.

Scientific Context: What 1,800 Cases Means in Historical Terms

The United States eliminated endemic measles in 2000. Since then, annual case counts above 1,000 have been rare events. The CDC recorded 1,282 cases in 2019, which was the highest total in 27 years at the time. A 2026 count approaching or exceeding 1,800 would represent the largest U.S. measles outbreak in the post-elimination era by a significant margin. Vaccination coverage gaps, concentrated in specific communities and geographic regions, are the primary structural driver. The market is not pricing a new scientific discovery. The market is pricing a public health reality that CDC data has been documenting since January.