The largest measles outbreak in the United States seems to be winding down. The South Carolina Department of Public Health says the state has now gone two full weeks without a new infection. Also, no one in the state is in quarantine or isolation for measles at this time, according to Brannon Traxler, MD, MPH, South Carolina’s chief medical officer.
There have been 997 reported cases of measles in South Carolina since the outbreak began in the Upstate region in October of last year.
Traxler told reporters today that the state will be able to officially declare the outbreak over on April 26, which will mark 42 days since the most recent case was identified. She explained that 42 is the "magic number,” as it is double the incubation period for measles, which ranges from 7 to 21 days.
The continued decline in cases is promising, said Traxler. However, her department remains concerned about unrecognized transmission.
“We remain vigilant for monitoring any potential cases and spread in our state, especially as many school districts across our state are taking spring break,” she said.
We remain vigilant for monitoring any potential cases and spread in our state.
Traxler said the state saw an acceleration of new cases following the winter holidays; therefore, there is some concern about measles transmission during spring break. She urges anyone susceptible to the measles virus to consider getting vaccinated. Immunization provides lifelong protection for roughly 97% of those who complete the two-dose series of the measles, mumps, and rubella vaccine.
Potential exposure at O’Hare
Elsewhere, the Chicago area is on alert after a potential measles exposure at O’Hare International Airport that occurred on March 24. The Cook County Department of Public Health says its communicable disease team has not identified any additional cases at this time.
O’Hare is the fourth-busiest publicly owned airport in the country, according to data published in 2025 by the Federal Aviation Administration. Airports are deeply challenging sites for measles exposure because of the number of people it’s possible to expose, Brown University epidemiologist Jennifer Nuzzo, DrPH, told CIDRAP News via email.
“Inflight exposures are relatively simple because there’s a passenger list, but exposures in the airport, where contacts are largely anonymous, are much harder,” she said.
