South Carolina's measles outbreak jumped to Washington state 5 times in 2 weeks

Key Points:

• Since measles was declared eliminated in the US in 2000, recent outbreaks are increasingly driven by domestic travel and under-vaccinated communities rather than international travelers, with vaccination rates declining nationwide.
• A Washington state study published in NEJM Evidence revealed that a large measles outbreak originating in South Carolina spread to Washington through five separate importation events in January, resulting in 26 cases before containment.
• The South Carolina outbreak, which began in October 2025 and ended in April 2026, recorded 997 cases, making it the largest US outbreak since elimination, though it has since been surpassed by an ongoing outbreak in Pennsylvania.
• Whole genome sequencing was crucial in distinguishing multiple distinct measles importations from South Carolina to Washington, highlighting the importance of genomic surveillance alongside traditional epidemiology in outbreak responses.
• The study contradicts claims by Health Secretary Robert F. Kennedy Jr. that the US measles surge is primarily due to a global outbreak and that the US is controlling it better than other countries; in reality, 96% of cases this year are linked to domestic outbreaks, with only 18 cases from international visitors.