The US is having its worst measles year since 1991, and Polymarket traders are still adjusting the odds on how much worse it gets.
As of Sept. 17, the CDC had confirmed 3,471 measles cases across 47 jurisdictions in 2026, already 52% ahead of the 2,289 cases recorded for all of 2025.
The Polymarket Odds
Polymarket runs a "Measles cases in U.S. in 2026?" market that has traded more than $8 million in volume since it opened on June 30, 2026. The market is structured as a ladder: each threshold is its own Yes/No line, resolving against the CDC's measles case counter through December 31, 2026.
| Threshold (cases) | Implied Yes Probability |
| 3,500+ | ~100% |
| 4,000+ | 99.7% |
| 4,500+ | 87% |
| 4,750+ | 81% |
| 5,000+ | 68% |
| 7,500+ | 14% |
| 10,000+ | 8.5% |
| 12,500+ | 3% |
*markets change quickly and exact probabilities referred to in this article may be out of date
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The market has effectively already settled that the US clears 4,000 cases this year. Where it's still genuinely split is the 5,000 line, priced at 68%, meaning traders see roughly a two-in-three chance the year finishes above it. Beyond that, the odds fall off fast. Getting to 7,500 cases is priced at just 14%, and 10,000 or more sits at 8.5%. Reaching 12,500, more than five times the 2025 full-year total, is down to 3%.
That drop-off matters. It implies traders think the current outbreak, driven heavily by Pennsylvania, will continue adding cases through year-end, but at a decelerating pace rather than the kind of exponential spread that would put six-figure or even five-figure case counts within reach.
Kalshi is also running its own measles prediction market. Stuck on choosing between the two platforms? Take a look at our reviews of the best prediction market apps.
Which States Carry the Most Risk?
Action Network built its own ranking to look at where new cases are most likely to show up next, combining each state's confirmed 2026 case rate with its kindergarten MMR vaccination coverage for the 2025-26 school year. Both figures were pulled from the CDC's measles data and its kindergarten vaccination coverage survey.
Each state's case rate per 100,000 kindergartners and its vaccination shortfall (lower coverage scores higher) were each scaled 0 to 100 and averaged into a single Index. States were then given an Implied Share of Risk, calculated by dividing each state's Index score by the combined Index score of all 50 scored jurisdictions.
That share is a relative risk measure, not a forecast of where the next case will land. It shows how the current outbreak and vaccination data are distributed across the country, not a calibrated probability of a specific outcome.
Highest risk share
| Rank | State | Measles Cases per 100k | Vaccination Rate | Index | Implied Share of Risk |
| 1 | Utah | 1,197.70 | 87.2% | 74.68 | 7.60% |
| 2 | South Carolina | 1,164.37 | 93.4% | 60.21 | 6.13% |
| 3 | Idaho | 18.41 | 75.2% | 50.77 | 5.17% |
| 4 | Wisconsin | 266.17 | 85.1% | 40.23 | 4.09% |
| 5 | North Dakota | 406.68 | 88.5% | 38.92 | 3.96% |
| 6 | Pennsylvania | 554.67 | 92.7% | 36.24 | 3.69% |
| 7 | Arizona | 148.84 | 87.4% | 30.47 | 3.10% |
| 8 | Minnesota | 28.37 | 85.7% | 29.03 | 2.95% |
| 9 | Ohio | 96.06 | 88.1% | 26.79 | 2.73% |
| 10 | Oregon | 150.10 | 89.6% | 25.89 | 2.63% |
Lowest risk share
| Rank | State | Measles Cases per 100k | Vaccination Rate | Index | Implied Share of Risk |
| 46 | New York City | 6.06 | 97.1% | 4.05 | 0.41% |
| 47 | Mississippi | 0.00 | 97.0% | 4.01 | 0.41% |
| 48 | New York | 23.59 | 97.7% | 3.52 | 0.36% |
| 49 | Connecticut | 9.06 | 98.6% | 1.01 | 0.10% |
| 50 | West Virginia | 12.95 | 98.9% | 0.54 | 0.05% |
Utah tops the ranking on the strength of its case rate, 527 confirmed cases against a kindergarten population of 44,001, which works out to roughly 1,198 cases per 100,000, by far the highest rate of any state scored. South Carolina and Idaho follow for different reasons: South Carolina's case rate is the second-highest in the country, while Idaho's ranking is driven almost entirely by its vaccination coverage, at 75.2%, the lowest of any state in the dataset. Pennsylvania, the site of the largest single outbreak feeding the national Polymarket market, ranks sixth once its higher vaccination coverage (92.7%) is weighed against its case count.
Kansas and Montana are excluded from the ranking. Both report no data for estimated MMR coverage or kindergarten population size in the CDC's 2025-26 survey.
Methodology
Action Network's state-by-state risk ranking uses two CDC data sets: the CDC's Measles Cases and Outbreaks data for confirmed case counts, and the CDC's Kindergarten Vaccination Coverage and Exemptions data for MMR coverage rates and kindergarten population size, both filtered to the 2025-26 school year.
The ranking covers 52 jurisdictions: all 50 states, DC, and New York City, which the CDC reports separately from New York State. Kansas and Montana are excluded from scoring, leaving 50 jurisdictions ranked. Both report no data for Estimated Percent Vaccinated or Population Size in the 2025-26 survey.
Case counts use only the 2026 year-to-date column, not a running total with 2024 or 2025 figures. The population figure used throughout is the kindergarten population size reported in the vaccination survey itself, not each state's total population.
From there:
- Measles Cases per 100k is each state's 2026 case count divided by its kindergarten population, multiplied by 100,000.
- Measles Cases per 100k normalized scales that figure 0 to 100 across all 50 scored jurisdictions, using min-max normalization.
- Vaccination rate normalized inverted does the same to each state's MMR coverage rate, then flips the scale so lower coverage produces a higher score.
- Index is the simple average of those two normalized scores.
- Rank orders jurisdictions by Index, descending. Rank 1 is the highest relative risk.
- Implied Share of Risk divides each state's Index by the combined Index of all 50 scored jurisdictions, so the column sums to 100%.
The Implied Share of Risk is a relative measure built from two normalized inputs. It is not a calibrated statistical probability that a given state will report a new confirmed case, and it should be read alongside the underlying case rate and vaccination figures rather than as a standalone forecast.
Dataset available on request.
