Five Separate Measles Importations Reached Washington in Two Weeks
Washington state recorded five distinct measles importations from South Carolina within two weeks in January, producing 26 cases, per a NEJM Evidence study.
The story in focus
A NEJM Evidence study by Washington state health officials found five separate measles importations from South Carolina reached Washington within two weeks in January, producing 26 cases. Whole-genome sequencing distinguished the introductions, and officials credit isolation, quarantine and contact tracing with containing spread.
- Five distinct importations from South Carolina reached Washington over two weeks in January, linked to 26 cases
- Whole-genome sequencing separated separate introductions from local transmission
- Clusters involved schools, healthcare facilities and a church
- South Carolina's outbreak ran October 2, 2025 to April 26, 2026 with 997 confirmed cases
- CDC data show 4,404 of 4,588 US measles cases this year are tied to domestic outbreaks
What the study found
Writing in NEJM Evidence, Washington state health officials described five separate introductions of measles from South Carolina into their state during two weeks in January. Together the importations led to 26 cases among Washington residents before spread was stopped.
The first involved a resident who developed a rash on January 12 after a trip to South Carolina and exposure to a sick person; one close contact fell ill and was isolated. A second event saw South Carolina visitors in public places while infectious, seeding a 14-case cluster from January 15 to February 17 that touched schools, healthcare facilities and a church. Two residents returning from South Carolina fell ill on January 15 and 16 with no further cases. A fourth traveler followed isolation and quarantine guidance, and no cases were linked. A fifth resident fell ill January 19 after out-of-state contact with ill people and visited a school and a healthcare facility, producing a seven-case cluster through January 29.
Sequencing and response
The authors said whole-genome sequencing supplemented epidemiological data, showing the cases came from multiple introductions rather than one that spread locally; sequences from five cases in the final cluster closely matched South Carolina sequences. Officials credited isolation, quarantine and contact tracing with limiting further spread.
Ars Technica reports that South Carolina's outbreak began October 2, 2025, was declared over April 26, 2026, and involved 997 confirmed cases. The report also cites CDC data showing 18 of 4,588 US measles cases this year were among international visitors, while 4,404 were linked to a domestic outbreak.
How many separate measles importations from South Carolina reached Washington state in January?
Five distinct importations arrived within two weeks in January, according to the NEJM Evidence study. They produced 26 cases in Washington, and whole-genome sequencing confirmed the separate introductions.
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