South Carolina Measles Outbreak Reached Washington in Five Importations, Study Finds

The study, reported by Ars Technica, describes how an outbreak that began in South Carolina on Oct. 2, 2025, and was declared over on April 26, 2026, traveled across the country. South Carolina confirmed 997 cases during the outbreak. At the time, it was the largest measles outbreak recorded since the virus was declared eliminated in the United States, though Pennsylvania’s ongoing outbreak has since surpassed it.

The study highlights the risk from domestic travel. Since measles was declared eliminated in the US in 2000, occasional cases have come mainly from international travelers—visitors from far-flung places where the virus still spreads freely—or unvaccinated US residents who return from abroad with a highly infectious souvenir. But as vaccination rates have slipped nationwide in recent years and outbreaks grow bigger and more frequent, domestic travel now poses a greater risk than international incursions, according to the study.

The five importations into Washington occurred over two weeks in January, the study says, and led to 26 cases among residents before officials stamped out the spread. The South Carolina outbreak was declared over in April 2026; Pennsylvania’s outbreak remains ongoing and has surpassed South Carolina’s 997 cases.