Most Washington counties fall short of measles herd immunity
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A measles outbreak this week in Snohomish County underscores broader vulnerability across Washington state, where vaccination coverage remains below protective levels.
Why it matters: Measles spreads more easily when vaccination rates fall below 95% — a herd immunity threshold only four of Washington's 39 counties met among kindergartners this past school year, according to state data.
By the numbers: Just 92.4% of King County kindergartners were vaccinated against measles in the 2024–25 school year, down from 95.6% in 2019–20.
- Snohomish County's rate was 92.2% last year, a two percentage-point drop since 2019–20.
- Statewide coverage was about 91%, trailing the national average of 92.5%.
Zoom in: The only Washington counties to reach 95% coverage among kindergartners in 2024–25 were Adams, Garfield, Wahkiakum and Yakima.
Context: Kindergarten vaccination rates are the state's most current indicator of immunization trends, reflecting the newest cohort entering classrooms.
The latest: The three new measles cases confirmed in Snohomish County this week were among children who weren't vaccinated against the disease, county health officials said.
- The children were exposed through a visiting family from South Carolina, where more than 500 cases have been reported.
- On Friday, the state Department of Health confirmed another case, which was also linked to travel to South Carolina. The patient was a Central Washington University student in Kittitas County, the health department said.
What they're saying: Public health officials say they expect the virus to spread further in Washington state, even as they try to contain it.
- "There are likely more cases in the community that we do not know about yet," Snohomish County Health Officer James Lewis said in a news release this week.
Threat level: Health officials are urging people who aren't immune to measles — or who aren't sure if they're vaccinated — to get the shot.
- "Measles is a serious disease that often brings unpleasant symptoms, and in rare cases swelling of the brain and even death," Kim Van Pelt, Snohomish County's health department director, said in a written statement.
What we're watching: Whether the outbreak pushes Washington's measles case count past last year's total of 12 — and how quickly.
Editor's note: This story has been updated to include new information about a measles case in Kittitas County.