The South Carolina Department of Public Health on Friday reported 310 measles cases linked to the ongoing outbreak in the state, an increase of 99 cases since earlier this week. This marks the sharpest rise in the outbreak since it began in October.
The outbreak remains concentrated in Upstate South Carolina, particularly in Spartanburg County, located in the northwest of the state.
A health department spokesperson said this is the largest spike in cases seen so far during the months-long outbreak.
Of the total cases, 256 patients were unvaccinated, two were partially vaccinated, and two were fully vaccinated with the recommended measles-mumps-rubella (MMR) vaccine. The vaccination status of 50 cases remains unknown.
Most infections have been reported among children aged five to 17, followed by children under five years old.
Health officials said 200 people are currently in quarantine, while nine are in isolation. The latest quarantine period is set to end on January 29.
State epidemiologist Dr. Linda Bell said the number of people in quarantine does not reflect the full extent of exposure. She warned that hundreds more people may have been exposed at public sites without realizing they should be in quarantine if they are not immune.
According to the US Centers for Disease Control and Prevention (CDC), a total of 2,144 measles cases were reported nationwide in 2025.
The World Health Organization (WHO) is expected to decide this year whether the United States will retain its measles elimination status. To maintain this status, a country must remain free of ongoing local transmission of the same measles strain for at least 12 months and maintain strong disease surveillance.
