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. 2022 Aug 24;75(1):e536-e544.
doi: 10.1093/cid/ciac279.

Associations Between Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Variants and Risk of Coronavirus Disease 2019 (COVID-19) Hospitalization Among Confirmed Cases in Washington State: A Retrospective Cohort Study

Miguel I Paredes  1   2 , Stephanie M Lunn  3 , Michael Famulare  4 , Lauren A Frisbie  3 , Ian Painter  3 , Roy Burstein  4 , Pavitra Roychoudhury  2   5 , Hong Xie  5 , Shah A Mohamed Bakhash  5 , Ricardo Perez  5 , Maria Lukes  5 , Sean Ellis  5 , Saraswathi Sathees  5 , Patrick C Mathias  5 , Alexander Greninger  2   5 , Lea M Starita  6   7 , Chris D Frazar  6 , Erica Ryke  6 , Weizhi Zhong  7 , Luis Gamboa  7 , Machiko Threlkeld  6 , Jover Lee  2 , Evan McDermot  7 , Melissa Truong  7 , Deborah A Nickerson  6   7 , Daniel L Bates  8 , Matthew E Hartman  8   9 , Eric Haugen  8 , Truong N Nguyen  8 , Joshua D Richards  8 , Jacob L Rodriguez  8 , John A Stamatoyannopoulos  8 , Eric Thorland  8 , Geoff Melly  3 , Philip E Dykema  3 , Drew C MacKellar  3 , Hannah K Gray  3 , Avi Singh  3 , JohnAric M Peterson  3 , Denny Russell  3 , Laura Marcela Torres  3 , Scott Lindquist  3 , Trevor Bedford  1   2   6   10 , Krisandra J Allen  3 , Hanna N Oltean  3
Affiliations

Associations Between Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Variants and Risk of Coronavirus Disease 2019 (COVID-19) Hospitalization Among Confirmed Cases in Washington State: A Retrospective Cohort Study

Miguel I Paredes et al. Clin Infect Dis. .

Abstract

Background: The coronavirus disease 2019 (COVID-19) pandemic is dominated by variant viruses; the resulting impact on disease severity remains unclear. Using a retrospective cohort study, we assessed the hospitalization risk following infection with 7 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants.

Methods: Our study includes individuals with positive SARS-CoV-2 reverse transcription polymerase chain reaction (RT-PCR) in the Washington Disease Reporting System with available viral genome data, from 1 December 2020 to 14 January 2022. The analysis was restricted to cases with specimens collected through sentinel surveillance. Using a Cox proportional hazards model with mixed effects, we estimated hazard ratios (HR) for hospitalization risk following infection with a variant, adjusting for age, sex, calendar week, and vaccination.

Results: In total, 58 848 cases were sequenced through sentinel surveillance, of which 1705 (2.9%) were hospitalized due to COVID-19. Higher hospitalization risk was found for infections with Gamma (HR 3.20, 95% confidence interval [CI] 2.40-4.26), Beta (HR 2.85, 95% CI 1.56-5.23), Delta (HR 2.28 95% CI 1.56-3.34), or Alpha (HR 1.64, 95% CI 1.29-2.07) compared to infections with ancestral lineages; Omicron (HR 0.92, 95% CI .56-1.52) showed no significant difference in risk. Following Alpha, Gamma, or Delta infection, unvaccinated patients show higher hospitalization risk, while vaccinated patients show no significant difference in risk, both compared to unvaccinated, ancestral lineage cases. Hospitalization risk following Omicron infection is lower with vaccination.

Conclusions: Infection with Alpha, Gamma, or Delta results in a higher hospitalization risk, with vaccination attenuating that risk. Our findings support hospital preparedness, vaccination, and genomic surveillance.

Keywords: COVID-19; SARS-CoV-2; hospitalization; vaccination; variants.

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Conflict of interest statement

Potential conflicts of interests. A. L. G. reports central testing lab contract from Abbott and research funding from Merck and Gilead. K. A. became an employee of Biobot Analytics after the initial manuscript submission. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Figure 1.
Figure 1.
Changing proportion of infections due to variant lineages in Washington over study period. Variant fraction is calculated from a 21-day rolling average from our full sequenced dataset spanning from 1 December 2020 to 14 January 2022 and normalized to 100% to better observe changes in proportion of infections from variant lineages compared to total infections.
Figure 2.
Figure 2.
Relative risk of hospitalization by variant lineage. Risk of hospitalization is compared to individuals infected with an ancestral lineage. Error bars represent 95% CI. Estimates are adjusted for age, sex assigned at birth, calendar week, and vaccination status. Abbreviation: CI, confidence interval.
Figure 3.
Figure 3.
HR for risk of hospitalization following infection with a VOC (excluding Beta due to small sample size) stratified by vaccination status. Unvaccinated individuals infected with ancestral lineages serve as the reference category for each VOC HR. Error bars represent 95% CI. Estimates are adjusted for calendar week, age and sex assigned at birth. Categories with less than 4 hospitalizations are censored. Abbreviations: CI, confidence interval; HR, hazard ratio; VOC, variant of concern.
Figure 4.
Figure 4.
Risk of hospitalization following Infection with Omicron vs Delta. A, Risk of hospitalization is compared to individuals infected with Delta. B, Unvaccinated individuals infected with Delta serve as the reference category for each VOC HR. Error bars represent 95% CI. Estimates are adjusted for calendar week, age and sex assigned at birth. Abbreviations: CI, confidence interval; VOC, variant of concern.
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