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About the COVID-19 data

About the data


Since January 21, 2020, Public Health – Seattle & King County has responded to an outbreak of novel coronavirus (COVID-19) in coordination with our partners at the Washington State Department of Health (DOH) and the Centers for Disease Control and Prevention (CDC). Timely and accurate local data are one of the cornerstones of our COVID-19 response, helping us inform policy decisions and identify communities most directly impacted by the virus.

Data sources

  • COVID-19 outcomes and immunizations data are from the Washington Department of Health.
  • Population estimates come from the 2020 Office of Financial Management and American Community Survey.

Reporting delays and limitations

Due to reporting delays (data lags), data is preliminary and subject to change. Data will be refreshed retrospectively with ongoing data quality improvements.

The following dates are used to report each COVID-19 metric:

  • Reported COVID-19 cases: specimen collection date from the first case-defining lab result
  • Hospitalizations due to COVID-19: hospital admission date for COVID-19 illness
  • Deaths due to COVID-19: date of death

Please also note that the data reflect reports for King County residents received through midnight the day before. Due to reporting delays, the following are considered incomplete and are excluded from our reports:

  • Cases: 3 most recent days
  • Hospitalizations: 4 most recent days
  • Deaths: 5 most recent days

Hospitalizations and death data

Hospitalizations and deaths are counted for individuals where the outcome was due to COVID-19 illness or were COVID-19 related. Hospitalization counts for recent days may include incidental COVID-19 hospitalizations (hospitalizations for injury or illness not primarily related to COVID-19). All hospitalizations are reviewed by our Disease Research Intervention Specialists and incidental hospitalizations are excluded. Counts on Mondays may include higher numbers of hospitalizations because review is not conducted over the weekend.

Washington State Department of Health and PHSKC implemented a new definition of COVID-associated deaths for any death that occurred on or after January 1, 2023. COVID-associated deaths are identified based on COVID-19 keywords listed on the death certificate and no longer require a positive COVID-19 PCR or antigen test result. This definition was adopted to align with national standards and guidance. Learn more about the updated death definition.

Before January 1, 2023, deaths among persons with positive COVID-19 PCR or antigen results were investigated to determine if the cause of death was confirmed or suspected to have been related to COVID-19. Death investigations were conducted by reviewing the decedent's death certificate and, when necessary, medical record information. If COVID-19 was ruled out as a cause of death, these deaths were removed from our dashboards and reports. Death certificates are typically filed within 2 weeks of the date of death; however, those can take up to a year to be finalized.

Average rates

The 7-day average rate is used to adjust for daily variations, which may be large among smaller populations. It is determined by first calculating the 7-day rate for each day in the past 28 days. Then, the average of the 7-day rates for the past 28 days is taken.

COVID-19 Community Levels versus Community Transmission

COVID-19 Community Levels are categories set by the CDC to determine the impact of COVID-19 on communities and actions to take. The CDC also provides Transmission Levels (also known as Community Transmission) to describe the amount of COVID-19 spread within each county.

The COVID-19 Community Level reported on the Current COVID-19 Metrics webpage may differ from what is reported on the CDC web page for several different reasons, including: (a) the Current COVID-19 Metrics web page uses the new COVID-19 admission rate and the percent of staffed inpatient beds occupied by COVID-19 patients for only King County, while the CDC web page uses these metrics for the Health Service Area (which includes other neighboring counties); (b) the new COVID-19 admissions rate on the Current COVID-19 Metrics web page excludes cases among people who are hospitalized for other reasons but also have COVID-19 (‘Incidental COVID-19 hospitalizations”), while the CDC web page includes these hospitalizations; (c) this web page is updated Wednesdays while the CDC web page is updated on Thursdays.

Age adjustment

When we compare rates of COVID-19 outcomes between different groups of people, we use age adjustment. Age adjustment is a common statistical method that accounts for differences in the age profiles between different groups to support a more representative comparison. This makes it easier to compare COVID-19 outcomes for different race and ethnicity groups even though some of the groups have more older or younger people than other groups.

Age adjustment is also helpful when we compare outcomes between groups of people with different vaccination statuses. The age profile of people who are up to date on vaccination can be very different than the age profile of people who are unvaccinated. This matters because older age groups have higher rates of vaccination, which protects them, and higher rates of other health conditions that put them at risk for more serious COVID-19 outcomes. Age adjusted rates provide a way to account for differences and compare groups meaningfully. Learn more about age adjustment.

Race and ethnicity

We calculate estimated rates for race and ethnicity. Individuals of Hispanic/Latina/o/x ethnicity, race/ethnicity are categorized as "Hispanic", while non-Hispanic/Latina/o/x ethnicity individuals are categorized as the race they selected. Individuals who selected multiple races are categorized as "multi-racial".

Sex and gender

The data on sex is representative of sex assigned at birth. Non-binary and gender diverse data are presented where available and is dependent of the data source. While we calculate rates for some sex and gender categories, we do not have population estimates – and therefore rates – for those who identify as non-binary.

COVID-19 phases

We refer to different changes of the COVID-19 pandemic as “phases.” A COVID-19 phase can refer to the timeframe when either 1) a SARS-CoV-2 variant was the dominant variant circulating across King County, 2) a new surge of COVID-19 infections, and/or 3) another significant change in the COVID-19 pandemic. Phases provide a way to compare different periods of the pandemic highlighting how COVID-19 outcomes have changed over time and how the current COVID-19 indicators compare to past time frames.

Phase name Start date End date
Winter 2020 phase January 1, 2020 June 17, 2020
Summer 2020 phase June 18, 2020 September 18, 2020
Fall 2020 phase September 19, 2020 February 28, 2021
Alpha phase March 1, 2021 July 7, 2021
Delta phase July 8, 2021 November 26, 2021
First Omicron phase November 27, 2021 March 27, 2022
Second Omicron phase March 28, 2022 November 11, 2022
Current phase
(Third Omicron phase)
November 12, 2022 Today

Vaccination status

Data from the Washington State Immunization Information System (WAIIS) are used to determine COVID-19 vaccine uptake and vaccination status for King County residents. Some visualizations use terms like "up to date" which currently refers to people who have received the recommended number of 2023-2024 updated vaccine doses. Find detailed information on COVID-19 vaccine recommendations from the CDC. More information on terms used in the dashboards can be found on the Download the data page.

Outcomes by vaccination status

Visualizations comparing outcomes by vaccination status show rates for each vaccination status, assessed at the time of an individual’s first positive COVID-19 test result for that disease event. While severe outcomes like hospitalization and death may occur days or weeks after the initial positive test date, a person’s vaccination status at the time of infection impacts their immune response. Most rates for outcomes by vaccination status are age-adjusted, except for charts comparing outcomes among age groups.

More details

Additional data notes are included on data dashboards.

More details on data definitions can be found on the Download the data page.