Measles Outbreak in South Carolina Spreads to Washington State

A measles outbreak in South Carolina that began in October 2025 has spread to Washington state through five distinct importation events over two weeks in January. According to a study published in NEJM Evidence, these events led to 26 cases among residents in Washington state before officials were able to stamp out the spread. The South Carolina outbreak, which was declared over on April 26, 2026, resulted in 997 confirmed cases, making it the largest measles outbreak recorded since the virus was declared eliminated in the US in 2000. The study highlights the risk of domestic travel in spreading the virus, as vaccination rates have slipped nationwide in recent years. The outbreak in South Carolina was initially caused by international travelers, but domestic travel now poses a greater risk than international incursions. The outbreak in Pennsylvania has since surpassed the one in South Carolina as the largest recorded since the virus was declared eliminated.