Sustained measles transmission across 32 states and New York City has produced 1,842 confirmed U.S. cases through early May 2026, already nearing the full-year 2025 total of 2,288 according to CDC surveillance. Primary drivers include declining MMR vaccination coverage—down to 92.5 percent among kindergartners—and clusters of unvaccinated individuals that sustain outbreaks, with 93 percent of 2026 cases linked to 25 active outbreaks and 92 percent occurring in unvaccinated or unknown-status persons. International importations and upcoming summer travel windows could accelerate spread before herd-immunity thresholds near 95 percent are restored. Weekly CDC case reports and the November elimination-status review will provide the next key data points for traders assessing whether annual totals exceed recent historical benchmarks.