Intrinsic and Effective Severity of Coronavirus Disease 2019 Cases Infected With the Ancestral Strain and Omicron BA.2 Variant in Hong Kong

Author:

Wong Jessica Y1ORCID,Cheung Justin K1,Lin Yun1,Bond Helen S1,Lau Eric H Y12,Ip Dennis K M1,Cowling Benjamin J12ORCID,Wu Peng12ORCID

Affiliation:

1. World Health Organization Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong , Hong Kong Special Administrative Region , China

2. Laboratory of Data Discovery for Health Limited, Hong Kong Science and Technology Park, New Territories , Hong Kong Special Administrative Region , China

Abstract

Abstract Background Understanding severity of infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants is crucial to inform public health measures. Here we used coronavirus disease 2019 (COVID-19) patient data from Hong Kong to characterize the severity profile of COVID-19. Methods Time-varying and age-specific effective severity measured by case hospitalization risk and hospitalization fatality risk was estimated with all individual COVID-19 case data collected in Hong Kong from 23 January 2020 through 26 October 2022 over 6 epidemic waves. The intrinsic severity of Omicron BA.2 was compared with the estimate for the ancestral strain with the data from unvaccinated patients without previous infections. Results With 32 222 COVID-19 hospitalizations and 9669 deaths confirmed over 6 epidemic waves, the time-varying hospitalization fatality risk dramatically increased from <10% before the largest fifth wave of Omicron BA.2 to 41% during the peak of the fifth wave when hospital resources were severely constrained. The age-specific fatality risk in unvaccinated hospitalized Omicron cases was comparable to the estimates for unvaccinated cases with the ancestral strain. During epidemics predominated by Omicron BA.2, fatality risk was highest among older unvaccinated patients. Conclusions Omicron has comparable intrinsic severity to the ancestral Wuhan strain, although the effective severity is substantially lower in Omicron cases due to vaccination.

Funder

Health and Medical Research Fund

Hong Kong Special Administrative Region (SAR) government

Collaborative Research Scheme

Research Grants Council

Hong Kong SAR government

RGC Senior Research Fellow Scheme

Hong Kong SAR

Publisher

Oxford University Press (OUP)

Subject

Infectious Diseases,Immunology and Allergy

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