The South Carolina Department of Public Health declared the Upstate measles outbreak over on April 26, after 42 consecutive days, two full incubation periods, without a new case linked to the cluster. The final tally is 997 confirmed cases dating to the first eight reported on October 2, 2025, with 940 of those cases in Spartanburg County, 21 hospitalizations, and no deaths. Of the 997 patients, 903 were children aged 17 or under, and 932 were unvaccinated or of unknown vaccination status, according to the state health department’s closing release.
It is the largest measles outbreak in the United States since 1991, when measles was still endemic and a Philadelphia outbreak associated with a faith-healing church killed nine children. South Carolina’s outbreak did not kill anyone, a point worth holding alongside the case count. Measles fatality in a contemporary U.S. setting runs between one and three deaths per 1,000 reported cases (CDC, “Measles: Complications,” updated 2025). At 997 cases, the absence of deaths is consistent with the lower end of that range and with the state’s hospital capacity to manage complications; it is not evidence that measles has become a mild disease.
What the outbreak data show, specifically
The Centers for Disease Control and Prevention’s Center for Forecasting and Outbreak Analytics published three scenario assessments during the outbreak, on January 2, January 20, and March 3, and the March 3 update is the most data-rich public document on the cluster’s structure. As of that date, 990 cases had been identified, with 945 (95 percent) classified as unvaccinated or of unknown vaccination status. Spartanburg County’s reported MMR coverage in schools stood at 88.9 percent, against a state average of 93.7 percent and a herd-protection threshold for measles that the World Health Organization and CDC both place at 95 percent. The CDC modeling team identified a single under-vaccinated community of roughly 15,000 people as the outbreak’s sustained transmission core.
Three points follow, and they should be kept distinct. First, the outbreak ended because transmission ran out of susceptible contacts within the affected community and because the public-health response (contact tracing, post-exposure prophylaxis, school exclusion, and a sharp local rise in MMR uptake) narrowed the susceptible pool further. Spartanburg County saw a 93 percent year-over-year increase in MMR vaccinations during the outbreak window, the state health department reported. Second, the outbreak did not end because measles became less contagious; the basic reproduction number for measles in a fully susceptible population is conventionally cited at 12 to 18, the highest of any human pathogen for which we have a stable estimate. Third, the underlying coverage gap that allowed the outbreak to begin has been narrowed in Spartanburg, but not closed, and the national picture has not changed.
The national picture, in numbers
The CDC’s national measles surveillance dashboard, last updated April 25, reports 1,884 confirmed cases in the United States for 2026 across 40 jurisdictions. The South Carolina cluster accounts for slightly more than half of that figure; an ongoing outbreak along the Utah–Arizona state line had reached more than 600 confirmed cases by mid-April and is still active. Twenty-two distinct outbreaks (defined as three or more linked cases) have been recorded so far this year, against a 2026 surveillance-period figure that already exceeds the full-year totals for every year between 2000 and 2024.
The U.S. measles elimination status, granted by the Pan American Health Organization in 2000, is contingent on the absence of endemic transmission for 12 consecutive months. The South Carolina outbreak began on October 2, 2025; the final South Carolina case was confirmed on March 15, 2026. If the Utah–Arizona cluster, which is a separate chain of transmission, runs continuously past October of this year, the elimination designation could be reviewed. PAHO’s next scheduled evaluation is later in 2026; the agency has not publicly stated a date. This is a procedural point about a label, not a statement about case severity, and the two should not be conflated.
A 93 percent jump in MMR uptake during an outbreak is what behavior change looks like in a crisis. It is not a substitute for routine coverage at the rate the disease requires. — Dr. Edward Simmer, Director, South Carolina Department of Public Health
What this outbreak does, and does not, tell us about vaccine policy
The Spartanburg cluster reproduces a pattern that the published literature on measles outbreaks since 2000 has documented repeatedly: a tightly clustered, under-vaccinated community sits below the herd-protection threshold; a single imported or unidentified-source case enters; sustained transmission follows for several months until contact-tracing and a vaccination surge bring the susceptible pool below sustaining capacity. The 2018–2019 outbreak in Rockland County and Brooklyn, New York, the 2014 outbreak in an Ohio Amish community, and the 2008 San Diego cluster all share the same epidemiological shape, documented in MMWR reports across those years.
What the South Carolina outbreak does not establish, by itself, is the effect of any specific federal policy change on national measles incidence. The Department of Health and Human Services revised its Advisory Committee on Immunization Practices charter in 2025, and the membership of the committee was reconstituted during the same period. Outbreak chains take months to play out, and the South Carolina cluster began before the most recent ACIP meetings concluded. To attribute the cluster to a policy change is to ignore the documented under-vaccination of the community of origin, which predates 2025; to deny any policy effect is to assume that vaccine-policy decisions have no bearing on the coverage trajectory the next outbreak will encounter. Both inferences run ahead of the data we currently have.
What to track
Three specifics are worth following in named sources. The Utah–Arizona cluster’s case curve, published by the Utah Department of Health and Human Services and the Arizona Department of Health Services on weekly schedules, is the most consequential active surveillance figure for the elimination question. The CDC’s national measles dashboard, updated weekly on Fridays, carries the running total. And the CDC Center for Forecasting and Outbreak Analytics has indicated it will publish a retrospective assessment of the Spartanburg cluster; that document, when issued, will be the first peer-adjacent characterization of the outbreak’s transmission tree, vaccination history, and response timing. Until then, the closing numbers from the South Carolina Department of Public Health are the record.