Measles Outbreak Spreads from South Carolina to Washington State

An outbreak of measles in South Carolina in 2025-2026 spread to Washington State through domestic travel, according to a study published in NEJM Evidence. The outbreak in South Carolina began on October 2, 2025, and was declared over on April 26, 2026. The outbreak resulted in 997 confirmed cases, making it the largest measles outbreak in the US since the virus was declared eliminated in 2000, although Pennsylvania's ongoing outbreak has since surpassed it.

The study highlights the risk of measles transmission through domestic travel, as five distinct importation events occurred over two weeks in January, leading to 26 cases in Washington State. The spread of measles from South Carolina to Washington State underscores the growing risk of domestic transmission as vaccination rates have declined nationwide in recent years.

Since the elimination of measles in the US in 2000, most cases have been linked to international travelers or unvaccinated US residents returning from abroad. However, the shift in the primary source of transmission to domestic travel poses a greater risk to public health.

Health officials in Washington State were able to contain the spread of measles, but the outbreak highlights the importance of maintaining high vaccination rates to prevent the spread of the virus. The study emphasizes the need for continued vigilance and public health measures to control the spread of measles and other infectious diseases.

In the context of the study, the outbreak in South Carolina was the largest since the virus was declared eliminated in 2000. The study also notes that the outbreak in Pennsylvania has since surpassed it in size. The spread of measles from South Carolina to Washington State through domestic travel highlights the importance of maintaining high vaccination rates and public health measures to prevent the spread of the virus.