New CDC surveillance data show measles transmission across the United States has more than doubled compared to last year, with South Carolina and Pennsylvania emerging as the two hardest-hit states in a year that has already seen national case counts climb well past 2025’s full-year pace. The figures, published through CDC’s National Notifiable Diseases Surveillance System (NNDSS) for the week ending September 12, 2026, put the year-to-date national total at 3,063 measles cases, compared to 1,374 cases reported through the same week in 2025, an increase of roughly 123%.
South Carolina and Pennsylvania account for a disproportionate share of this year’s national total. South Carolina leads all states with 686 cumulative cases so far in 2026, up from just 1 case reported through the same week last year. Pennsylvania follows closely behind with 649 cases in 2026, compared to only 12 at this point in 2025. Together, these two states alone account for roughly 44% of all indigenous measles cases reported nationally this year. Utah rounds out the states with the largest 2026 totals, reporting 531 cumulative cases, up sharply from 27 last year.
The current week’s data underscore that Pennsylvania’s outbreak remains very much active: of the 101 new indigenous measles cases reported nationally for the week ending Sep. 12, 76 were in Pennsylvania alone, with the state’s Middle Atlantic region accounting for 85 of the week’s total cases when combined with neighboring New York.
Beyond these three leading states, Virginia has recorded 178 cases so far this year, up from just 1 last year, while Arizona, despite reporting fewer weekly cases recently, still shows 24 cumulative cases in 2026 compared to 39 in all of 2025. Meanwhile, some regions that drove case counts in 2025 have seen substantial declines: Texas, which accounted for 787 of the nation’s 1,374 cases through week 36 of last year, the largest single-state contributor in 2025, has reported just 170 cases so far in 2026.
Case counts in the NNDSS data base are submitted voluntarily by state, territorial, and local health departments, and are subject to revision as delayed or corrected reports come in; finalized annual totals often differ somewhat from the weekly provisional figures. Measles is a nationally notifiable disease in nearly all jurisdictions, however, which generally makes case ascertainment more complete than for some other conditions on the NNDSS list, given the disease’s high visibility, clinical presentation, and established outbreak-response protocols.
Sustained indigenous transmission at this scale, concentrated in specific states rather than distributed evenly nationwide, is typically the pattern public health officials associate with localized pockets of under-vaccination reaching a threshold sufficient to sustain ongoing community spread.
Sources and further reading:
Measles, Indigenous — Weekly cases of notifiable diseases, United States, U.S. Territories, and Non-U.S. Residents, week ending September 12, 2026. CDC National Notifiable Diseases Surveillance System
This article was researched and sourced by Global Biodefense editors and reported with Claude AI assistance for drafting and editing.