A measles outbreak in upstate South Carolina has forced more than 150 unvaccinated children out of the classroom and into quarantine, state health officials said.

The South Carolina Department of Public Health said in an Oct. 9 briefing that the state has recorded its 11th measles case of the year, after a new infection was confirmed in a child from Greenville County, the state’s most populous county.

“What this new case tells us is that there is active, unrecognized community transmission of measles occurring,” said Dr. Linda Bell, South Carolina’s state epidemiologist.

Eight of the state’s cases have been linked to two schools in neighboring Spartanburg County, one public elementary school and one public K-12 charter school.

According to Bell, 153 students who were exposed and lack vaccination have been ordered to quarantine for 21 days, the longest incubation period for the measles virus.

“Those schools are following the protocols to exclude these students until the period of potential disease transmission has safely ended,” she said in the briefing.

“Those students are identified as having been exposed and not having been vaccinated, and that’s the reason for the exclusion.

“Those measures will help us be effective in preventing the spread of measles virus in those schools and in our communities.”

None of the 11 people infected in South Carolina had been vaccinated for the disease, according to the state health department. The department also urged anyone without immunity who may have been exposed to quarantine themselves and monitor for symptoms such as fever, cough, or rash.

Spartanburg County has one of the lowest vaccination rates in the state. Health department data show that, for the past 2024–2025 school year, less than 90 percent of students there received their required immunizations, including the two-dose MMR vaccine series.

Health officials are also investigating whether the new case reported in Greenville County is connected to the Spartanburg outbreak.

Nationwide, the Centers for Disease Control and Prevention has confirmed 1,563 measles cases in 2025 as of Oct. 7. Most infections have been linked to outbreaks within the United States, though 21 cases were reported among international visitors.

Federal officials maintain that the MMR vaccine remains the most effective defense against measles. The vaccination process includes two doses of vaccine containing live, attenuated measles, mumps, and rubella virus.

“The most effective way to prevent the spread of measles is the MMR vaccine,” Health Secretary Robert F. Kennedy Jr. wrote earlier this year in a post on X. Kennedy also detailed the federal response to a major measles outbreak in Texas, including deploying a CDC team to supply MMR vaccines and other medical supplies to pharmacies and state-run clinics.

Texas declared its outbreak over on Aug. 18 after 42 days without new cases. That outbreak, centered in West Texas, resulted in 762 confirmed infections, 99 hospitalizations, and the deaths of two school-aged children since it began in late January.