Estimated COVID-19 outcomes averted by primary vaccine series among King County, Washington residents, February - September 2021: a retrospective modelling study of surveillance data.
6 affiliations
- 1Public Health - Seattle & King County, Seattle, Washington, USA. [email protected].
- 2Public Health - Seattle & King County, Seattle, Washington, USA. [email protected].
- 3Public Health - Seattle & King County, Seattle, Washington, USA.
- 4Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, Washington, USA.
- 5Division of Infectious Diseases, Department of Pediatrics, University of Washington, Seattle, Washington, USA.
- 6Department of Epidemiology, University of Washington, Seattle, Washington, USA.
Abstract
Background
The initial monovalent coronavirus disease 2019 (COVID-19) vaccines were highly effective against severe COVID-19 outcomes. Robust estimates of the number of adverse health outcomes averted by the first phase of vaccination show the potential population-level impact of vaccine uptake and can inform future policy and planning decisions. In this modelling study, we estimate the number of COVID-19 hospitalizations and deaths in King County, Washington averted by primary series vaccination across the first eight months of uptake (February 2021 - September 2021).Methods
This study used surveillance data on hospitalizations and deaths due to COVID-19 from February 2021 through September 2021 for all King County residents 12 years and older. Data were reported routinely to the Washington State Department of Health. Outcomes were manually reviewed by Public Health-Seattle & King County and incidental hospitalizations and deaths were excluded, resulting in robust identification of outcomes due to COVID-19. We estimated outcomes averted by calculating the rate difference between vaccinated and unvaccinated groups for COVID-19 hospitalizations and deaths, and then applying the rate difference to the number of vaccinated individuals susceptible to COVID-19. Results were calculated by day and age group, then aggregated across the full study period for total counts.Results
There were 3,086 recorded COVID-19 hospitalizations and 591 COVID-19 deaths among King County residents ages 12 years and older during the study period. In this modelling framework, we estimate 16,607 COVID-19 hospitalizations and 4,307 deaths averted by vaccination during the same period. In the absence of vaccination, the number of COVID-19 hospitalizations would have been over six times greater than was observed, and the number of COVID-19 deaths nearly eight times greater.Conclusions
This study estimates that primary COVID-19 vaccination had a substantial impact on COVID-19 outcomes at the population level in King County, Washington. The validity of our estimates is uniquely strengthened by a rigorous definition of hospitalizations due to COVID-19. Local health jurisdictions can utilize these methods to illustrate the impact of vaccination efforts and inform resource allocation at the local level.
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BibTeX
@article{lau2026estimated,
title = {{Estimated COVID-19 outcomes averted by primary vaccine series among King County, Washington residents, February - September 2021: a retrospective modelling study of surveillance data.}},
author = {Kathryn M Lau and Katrin E Fabian and Meaghan S Fagalde and Libby C Page and Sargis Pogosjans and Eric J Chow},
journal = {BMC public health},
year = {2026},
month = aug,
doi = {10.1186/s12889-026-28801-3},
url = {https://europepmc.org/article/MED/42968025},
note = {CC BY-NC-ND},
}
RIS
TY - JOUR
TI - Estimated COVID-19 outcomes averted by primary vaccine series among King County, Washington residents, February - September 2021: a retrospective modelling study of surveillance data.
AU - Kathryn M Lau
AU - Katrin E Fabian
AU - Meaghan S Fagalde
AU - Libby C Page
AU - Sargis Pogosjans
AU - Eric J Chow
PY - 2026
DA - 2026/08/05
JO - BMC public health
DO - 10.1186/s12889-026-28801-3
UR - https://europepmc.org/article/MED/42968025
AB - Background The initial monovalent coronavirus disease 2019 (COVID-19) vaccines were highly effective against severe COVID-19 outcomes. Robust estimates of the number of adverse health outcomes averted by the first phase of vaccination show the potential population-level impact of vaccine uptake and can inform future policy and planning decisions. In this modelling study, we estimate the number of COVID-19 hospitalizations and deaths in King County, Washington averted by primary series vaccination across the first eight months of uptake (February 2021 - September 2021).Methods This study used surveillance data on hospitalizations and deaths due to COVID-19 from February 2021 through September 2021 for all King County residents 12 years and older. Data were reported routinely to the Washington State Department of Health. Outcomes were manually reviewed by Public Health-Seattle & King County and incidental hospitalizations and deaths were excluded, resulting in robust identification of outcomes due to COVID-19. We estimated outcomes averted by calculating the rate difference between vaccinated and unvaccinated groups for COVID-19 hospitalizations and deaths, and then applying the rate difference to the number of vaccinated individuals susceptible to COVID-19. Results were calculated by day and age group, then aggregated across the full study period for total counts.Results There were 3,086 recorded COVID-19 hospitalizations and 591 COVID-19 deaths among King County residents ages 12 years and older during the study period. In this modelling framework, we estimate 16,607 COVID-19 hospitalizations and 4,307 deaths averted by vaccination during the same period. In the absence of vaccination, the number of COVID-19 hospitalizations would have been over six times greater than was observed, and the number of COVID-19 deaths nearly eight times greater.Conclusions This study estimates that primary COVID-19 vaccination had a substantial impact on COVID-19 outcomes at the population level in King County, Washington. The validity of our estimates is uniquely strengthened by a rigorous definition of hospitalizations due to COVID-19. Local health jurisdictions can utilize these methods to illustrate the impact of vaccination efforts and inform resource allocation at the local level.
SN - 1471-2458
ER -