South Carolina public health officials have formally ended a measles outbreak that sickened 997 people over a six-month period, state authorities said. The outbreak, which began in October 2025, spread predominantly among largely unvaccinated school-age children and became the largest single-location outbreak in the United States since measles was considered eliminated.
State records show the last reported case occurred on March 15. Officials observed a 42-day waiting period following that report - equal to twice the virus's maximum incubation period - before declaring the outbreak over, in keeping with public health protocols. The U.S. Centers for Disease Control and Prevention assisted state health authorities during the response, including work to analyse case data.
Of the 997 infections recorded in South Carolina, 932 were in people who had never received a measles vaccine. Spartanburg County bore the brunt of the outbreak, accounting for more than 90% of infections. Children between the ages of 5 and 17 represented the largest single age group affected, with 639 cases among that cohort.
The direct cost of responding to the outbreak was estimated at $2.1 million for the state. During the response, public health and school officials required 874 students to quarantine across 33 schools, a disruption that followed the concentration of cases among school-age children.
Officials also reported a marked increase in measles vaccinations statewide as a result of the response. More than 81,000 vaccine doses were administered across South Carolina, representing a 31% increase compared with doses given in 2025.
The outbreak occurred against a backdrop of rising measles activity nationally. The United States reported 2,288 confirmed measles cases in 2025, the highest annual total since 1991, according to the CDC, and had recorded 1,792 cases so far this year as of April 23. Measles had been declared eliminated in the U.S. in 2000 - a designation indicating the virus was no longer spreading continuously within the country - but that elimination status is under review, with the Pan American Health Organisation delaying a decision until November.
State and federal health authorities coordinated through the response and followed established protocols for declaring the outbreak over after the required period without additional cases. The data released by officials highlights the concentration of cases among unvaccinated individuals and the substantial public health resources deployed to contain the outbreak.