Flu season in Pacific Northwest: Rainy winters keep people inside; Alaska plays by different rules
Seattle and Portland's legendary rainy winters create long months of indoor crowding — not through cold, but through wet. From October through April, most outdoor activities move inside, and the result looks a lot like a Midwestern winter in terms of indoor crowding patterns. Washington State's tech sector adds dense office environments to the mix. And then there's Alaska: geographically vast, with remote villages that can go weeks without flu, and then see it burn through an isolated community in days once it arrives.
Current flu activity — HHS Region 10
This data is pulled live from the Delphi CMU Epidata API, which mirrors CDC FluView ILINet data for HHS Region 10. It reflects the most recent week available — typically data through the prior Saturday, published by the CDC the following Thursday.
States in HHS Region 10
HHS Region 10 covers Alaska, Idaho, Oregon, and Washington. These states are grouped together by the Department of Health and Human Services for federal health program administration, and the CDC uses the same regional boundaries for flu surveillance reporting. ILI activity data is aggregated across all ILINet providers in the region, so the number reflects the regional average — individual states can vary significantly.
When flu typically peaks here
HHS Region 10 is consistently one of the last regions to peak, with flu typically reaching its high point in mid-to-late February. Some years — particularly when the national season is late — the peak can extend into early March in parts of Alaska and rural Idaho. The West Coast lag that affects Region 9 applies here too, though the rainy Pacific Northwest winters mean indoor crowding starts earlier than in California, which can slightly accelerate onset compared to Region 9.
Washington State typically leads the region, with the Seattle-Tacoma metro (Puget Sound) showing activity first. Oregon and the Portland metro follow a week to ten days later. Idaho runs its own pattern — the Boise metro tracks more like the Mountain region than the Pacific Northwest, while northern and eastern Idaho's rural communities can lag significantly.
Alaska is the most difficult state in the country to characterize with ILI data. Anchorage and Fairbanks are well-represented in surveillance; rural Bush Alaska communities are not. Flu outbreaks in remote Alaskan villages can be severe — some of the highest flu hospitalization rates in the country occur in Alaska Native communities — but these don't always show up in the regional ILI percentage because of limited provider reporting from remote areas.
What drives Pacific Northwest flu patterns
Rain-driven indoor crowding in western WA and OR. Seattle averages 150 rainy days per year; Portland, 145. Unlike cold-driven indoor crowding, rain-driven crowding starts earlier in the fall (October vs. November-December in colder regions) and continues through spring. The Pacific Northwest's rainy season aligns almost perfectly with flu season, making it one of the most efficient environments for sustained transmission.
Tech sector office density. The Seattle metro is home to Amazon, Microsoft, Costco, Starbucks, Boeing, and hundreds of tech companies. High-density office campuses with centralized HVAC are efficient flu transmission environments. Microsoft's Redmond campus alone employs tens of thousands on a single connected campus. Tech sector transmission clusters are identifiable in contact-tracing data during high-activity weeks.
Idaho's rural-conservative dynamic. Idaho consistently shows among the lowest flu vaccination rates of any Pacific Northwest state. Rural Idaho's skepticism of public health recommendations, combined with limited primary care access, means flu spreads further before people seek treatment. The ILI data from Idaho underrepresents true community activity.
Alaska Native communities' unique vulnerability. Alaska Native populations experience flu hospitalization and mortality rates significantly above national averages. Geographic isolation, overcrowded housing in some villages, and limited access to both vaccines and antivirals within the 48-hour treatment window all contribute. The state has made sustained efforts to improve vaccine distribution in rural communities, with measurable improvement over the past decade.
Recent seasons in HHS Region 10
Regional peak timing and severity can vary substantially from the national picture. The table below shows Region 10-specific peak months and severity for recent seasons, based on CDC FluView regional ILI data.
| Season | Regional peak | Dominant strain | Severity | Notable |
|---|---|---|---|---|
| 2024–25 | February | H3N2 / H1N1 | High | Above-average; Seattle peaked mid-February; Alaska Native communities severely affected |
| 2023–24 | February | H1N1 | Moderate | Moderate season; Pacific Northwest lag intact; Oregon followed WA by ~8 days |
| 2022–23 | January–February | H3N2 | High | Early national season; Region 10 still peaked in February |
| 2021–22 | March | H3N2 | Moderate | Unusually late; some Pacific NW areas peaked in March |
| 2019–20 | February | H1N1 | High | Typical timing; ended with COVID-19 in March before full decline |
For Alaska residents outside Anchorage and Fairbanks: the regional ILI number doesn't represent you. Rural Bush Alaska has historically seen flu outbreaks that are far more severe than the regional or state averages suggest. IHS and tribal health systems are your best local data source. Vaccination is especially important in communities where antivirals may take days to arrive. Track national and regional activity. →
How to use this data
The live activity level above reflects the most recent week of CDC ILINet data for Region 10. There is always roughly a one-week lag between real-world conditions and published numbers — providers report weekly, the CDC publishes Thursdays, and this page reflects those numbers. During a rapidly rising season, treat the current level as a floor.
The ILI percentage is the share of outpatient visits attributed to influenza-like illness across all ILINet reporting providers in the region. It is not a case count and does not capture people who don't seek care. In regions with lower healthcare utilization rates (rural areas, communities with limited access), ILI percentages tend to understate true community activity.
For the most complete picture of the current season — including strain typing, lab positivity trends, and hospitalization data — the IsItFluSeasonYet homepage shows all of this in context. The regional activity shown here is the same data source as the homepage's region breakdown.