The illness generally appears seven to 14 days after exposure, though it can take as long as 21 days (which is the length of quarantine). When it does appear, it features a high fever and a characteristic rash that begins on the head and moves downward. People can spread the virus for four days before the rash shows up and for four days after it emerges. Complications range from ear infections and diarrhea to encephalitis (brain swelling), pneumonia, death in up to 3 out of 1,000 children, and, in very rare instances, a deadly neurological condition that can develop seven to 10 years after the initial infection (subacute sclerosing panencephalitis).
Two doses of the measles, mumps, and rubella (MMR) vaccine are about 97 percent effective against measles, and that immunity is regarded as lifelong. Ninety-nine percent of the 310 cases in the South Carolina outbreak are among people who are unvaccinated, partially vaccinated, or have unknown vaccination status (only 2 people were vaccinated).
The Centers for Disease Control and Prevention, which only has data as of January 6, has counted three confirmed cases so far this year (two in South Carolina and one in North Carolina linked to the South Carolina outbreak). Since then, South Carolina reported 26 cases on Tuesday and 99 today, bringing its total to 125. North Carolina also reported three additional cases Tuesday, again tied to the South Carolina outbreak. Altogether, that raises the U.S. total to at least 131 just nine days into the year.
In 2025, the country recorded 2,144 confirmed cases, the highest number since 1991. Three people died, including two otherwise-healthy children. The U.S. declared measles eliminated in 2000, meaning it was no longer continuously circulating domestically. Continued outbreaks, such as the one in South Carolina, threaten that elimination status.
