Intrinsic and Effective Severity of Coronavirus Disease 2019 Cases Infected With the Ancestral Strain and Omicron BA.2 Variant in Hong Kong
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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.
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Omicron variants, although more infective, are associated with lower rates of hospitalization and death compared with previous SARS-CoV-2 strains.
“Omicron variants, although more infective, are associated with lower rates of hospitalization and death compared with previous SARS-CoV-2 strains.”
From An Omicron-specific, self-amplifying mRNA booster vaccine for COVID-19: a phase 2/3 randomized trial (2024) · cites this paper as [27]
The Results (page unavailable) report lower case-hospitalization risk in Omicron-predominant wave 5 than in earlier waves for adults aged 45 and older. But they report higher fatality risk among hospitalized older adults in wave 5, while the Discussion finds Omicron BA.2 and the ancestral strain had similar intrinsic severity. The paper attributes lower effective severity to vaccination and does not establish the claim that Omicron variants are more infective. (LLM, conf=0.88)
Experimental — accuracy not yet measuredStudies have shown that the intrinsic severity of the Omicron variant is similar to that of its predecessors and cross-reactive protection from vaccination and/or infection plays an important role in reducing the severity of Omicron-associated COVID-19.
“Studies have shown that the intrinsic severity of the Omicron variant is similar to that of its predecessors and cross-reactive protection from vaccination and/or infection plays an important role in reducing the severity of Omicron-associated COVID-19 (ref. 27).”
From An Omicron-specific, self-amplifying mRNA booster vaccine for COVID-19: a phase 2/3 randomized trial (2024) · cites this paper as [27]
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Cites
Rapid epidemic expansion of the SARS-CoV-2 Omicron variant in southern Africa
Viana, R. P. E. S., Moyo, S. M., Amoako, D. G., Tegally, H., Scheepers, C., Althaus, C. L., Anyaneji, U. J., Bester, P. A., Boni, M. F., Chand, M., et al. (2022) · Nature · doi:10.1038/s41586-022-04411-y · Cited by 1,653 · see citing works
Cowling, B. J., Ali, S. T., Ng, T. W. Y., Tsang, T. K., Li, J. C. M., Fong, M. W., Liao, Q., Kwan, M. Y., Lee, S. L., Chiu, S. S., et al. (2020) · The Lancet Public Health · doi:10.1016/s2468-2667(20)30090-6 · Cited by 1,258 · see citing works
Self-citationNyberg, T., Ferguson, N. M., Nash, S. G., Webster, H. H., Flaxman, S., Andrews, N., Hinsley, W., Bernal, J. L., Kall, M., Bhatt, S., et al. (2022) · The Lancet · doi:10.1016/s0140-6736(22)00462-7 · Cited by 1,221 · see citing works
Nyberg, T., Ferguson, N. M., Nash, S., Webster, H. H., Flaxman, S. R., Andrews, N. J., Hinsley, W. R., Bernal, J. L., Kall, M. M., Bhatt, S., et al. (2022) · Northumbria Research Link (Northumbria University) · doi:10.17863/cam.81883 · Cited by 1,129 · see citing works
Wolter, N., Jassat, W., Walaza, S., Welch, R., Moultrie, H., Groome, M., Amoako, D. G., Everatt, J., Bhiman, J. N., Scheepers, C., et al. (2022) · The Lancet · doi:10.1016/s0140-6736(22)00017-4 · Cited by 1,041 · see citing works
Levin, A. T., Hanage, W. P., Owusu-Boaitey, N., Cochran, K. B., Walsh, S. P., & Meyerowitz-Katz, G. (2020) · European Journal of Epidemiology · doi:10.1007/s10654-020-00698-1 · Cited by 844 · see citing works
McMenamin, M. E., Nealon, J., Lin, Y., Wong, J. Y., Cheung, J. K., Lau, E. H. Y., Wu, P., Leung, G. M., & Cowling, B. J. (2022) · The Lancet Infectious Diseases · doi:10.1016/s1473-3099(22)00345-0 · Cited by 360 · see citing works
Self-citationWong, C. K. H., Au, I. C. H., Lau, K. T. K., Lau, E. H. Y., Cowling, B. J., & Leung, G. M. (2022) · The Lancet · doi:10.1016/s0140-6736(22)01586-0 · Cited by 299 · see citing works
Self-citationWong, C. K. H., Au, I. C. H., Lau, K. T. K., Lau, E. H. Y., Cowling, B. J., & Leung, G. M. (2022) · The Lancet Infectious Diseases · doi:10.1016/s1473-3099(22)00507-2 · Cited by 269 · see citing works
Self-citationJassat, W., Karim, S. S. A., Mudara, C., Welch, R., Ozougwu, L., Groome, M. J., Govender, N., von Gottberg, A., Wolter, N., Wolmarans, M., et al. (2022) · The Lancet Global Health · doi:10.1016/s2214-109x(22)00114-0 · Cited by 233 · see citing works
Tsang, T. K., Wu, P., Lin, Y., Lau, E. H. Y., Leung, G. M., & Cowling, B. J. (2020) · The Lancet Public Health · doi:10.1016/s2468-2667(20)30089-x · Cited by 204 · see citing works
Self-citationAnalysis of Hospital Resource Availability and COVID‐19 Mortality Across the United States
Janke, A. T., Mei, H., Rothenberg, C., Becher, R. D., Lin, Z., & Venkatesh, A. K. (2021) · Journal of Hospital Medicine · doi:10.12788/jhm.3539 · Cited by 169 · see citing works
Xiao, J., Cheung, J. K., Wu, P., Ni, M. Y., Cowling, B. J., & Liao, Q. (2022) · The Lancet Regional Health - Western Pacific · doi:10.1016/j.lanwpc.2022.100441 · Cited by 146 · see citing works
Self-citationChallenges in Inferring Intrinsic Severity of the SARS-CoV-2 Omicron Variant
Bhattacharyya, R. P., & Hanage, W. P. (2022) · New England Journal of Medicine · doi:10.1056/nejmp2119682 · Cited by 143 · see citing works
Epidemiology of Infections with SARS-CoV-2 Omicron BA.2 Variant, Hong Kong, January–March 2022
Mefsin, Y. M., Chen, D., Bond, H. S., Lin, Y., Cheung, J. K., Wong, J. Y., Ali, S. T., Lau, E. H. Y., Wu, P., Leung, G. M., et al. (2022) · Emerging infectious diseases · doi:10.3201/eid2809.220613 · Cited by 142 · see citing works
Self-citationInfection Fatality Risk of the Pandemic A(H1N1)2009 Virus in Hong Kong
Wong, J. Y., Wu, P., Nishiura, H., Goldstein, E., Lau, E. H. Y., Yang, L., Chuang, S. K., Tsang, T., Peiris, M. J. S., Wu, J. T. K., et al. (2013) · American Journal of Epidemiology · doi:10.1093/aje/kws314 · Cited by 94 · see citing works
Self-citationTo, K. K., Cheng, V. C., Cai, J., Chan, K., Chen, L., Wong, L. S., Choi, C. Y.-K., Fong, C. H.-Y., Ng, A. C., Lu, L., et al. (2020) · The Lancet Microbe · doi:10.1016/s2666-5247(20)30053-7 · Cited by 90 · see citing works
Hui, K. P. Y., Ng, K., Ho, J. C., Yeung, H.-W., Ching, R. H. H., Gu, H., Chung, J. C. K., Chow, V. L. Y., Sit, K., Hsin, M. K. Y., et al. (2022) · EBioMedicine · doi:10.1016/j.ebiom.2022.104232 · Cited by 88 · see citing works
Dang, A. T., Thakker, R. A., Li, S., Hommel, E. L., Mehta, H. B., & Goodwin, J. S. (2022) · JAMA Network Open · doi:10.1001/jamanetworkopen.2022.1754 · Cited by 78 · see citing works
Increased risk of hospitalisation and death with the delta variant in the USA
Bast, E. S., Tang, F., Dahn, J. R., & Palacio, A. (2021) · The Lancet Infectious Diseases · doi:10.1016/s1473-3099(21)00685-x · Cited by 74 · see citing works
A Frail Health Care System for an Old Population: Lesson form the COVID-19 Outbreak in Italy
Volpato, S., Landi, F., & Incalzi, R. A. (2020) · The Journals of Gerontology Series A · doi:10.1093/gerona/glaa087 · Cited by 54 · see citing works
Gray, W. K., Navaratnam, A. V., Day, J., Wendon, J. A., & Briggs, T. W. R. (2021) · Thorax · doi:10.1136/thoraxjnl-2021-218025 · Cited by 52 · see citing works
Song, Z., Zhang, X., Patterson, L. J., Barnes, C. L., & Haas, D. A. (2021) · JAMA Health Forum · doi:10.1001/jamahealthforum.2021.4223 · Cited by 46 · see citing works
Impact of Severe Acute Respiratory Syndrome Coronavirus 2 Variants on Inpatient Clinical Outcome
Robinson, M. L., Morris, C. P., Betz, J., Zhang, Y., Bollinger, R. C., Wang, N., Thiemann, D. R., Fall, A., Eldesouki, R. E., Norton, J. M., et al. (2022) · Clinical Infectious Diseases · doi:10.1093/cid/ciac957 · Cited by 42 · see citing works
Hospitalization Fatality Risk of Influenza A(H1N1)pdm09: A Systematic Review and Meta-Analysis
Wong, J. Y., Kelly, H. A., Cheung, C.-M. M., Shiu, E. Y. C., Wu, P., Ni, M. Y., Ip, D., & Cowling, B. J. (2015) · American Journal of Epidemiology · doi:10.1093/aje/kwv054 · Cited by 37 · see citing works
Self-citationGreene, S. K., Levin‐Rector, A., Kyaw, N. T. T., Luoma, E., Amin, H., McGibbon, E., Mathes, R. W., & Ahuja, S. D. (2022) · Influenza and Other Respiratory Viruses · doi:10.1111/irv.13062 · Cited by 28 · see citing works
Age-Dependent Effects of COVID-19 Vaccine and of Healthcare Burden on COVID-19 Deaths, Tokyo, Japan
Ko, Y. K., Murayama, H., Yamasaki, L., Kinoshita, R., Suzuki, M., & Nishiura, H. (2022) · Emerging infectious diseases · doi:10.3201/eid2809.220377 · Cited by 16 · see citing works
Reichert, E. N., Schaeffer, B., Gantt, S., Rumpler, É., Govender, N., Welch, R., Shonhiwa, A. M., Iwu, C. D., Lamola, T. M., Moema-Matiea, I., et al. (2022) · The Lancet Microbe · doi:10.1016/s2666-5247(22)00182-3 · Cited by 8 · see citing works
Brizzi, A., Whittaker, C., Servo, L. M. S., Hawryluk, I., Junior, C. A. P., de Souza, W. M., Aguiar, R. S., de Araújo, L. J. T., Bastos, L. S., Blenkinsop, A., et al. (2022) · Nature Medicine · doi:10.1038/s41591-022-01939-4 · Cited by 3 · see citing works
Real-time estimation of the hospitalization fatality risk of influenza A(H1N1)pdm09 in Hong Kong
Wong, J. Y., Wu, P., Lau, E. H. Y., Tsang, T. K., FANG, V. J., Ho, L., & Cowling, B. J. (2015) · Epidemiology and Infection · doi:10.1017/s0950268815003179 · Cited by 1 · see citing works
Self-citation
Flagged first, then by citations
Cited by
Sorted by citations
Hanage, W. P., & Schaffner, W. (2024) · Infectious Diseases and Therapy · doi:10.1007/s40121-024-01080-4 · Cited by 80 · see citing works
An Omicron-specific, self-amplifying mRNA booster vaccine for COVID-19: a phase 2/3 randomized trial
Saraf, A., Gurjar, R., Kaviraj, S., Kulkarni, A., Kumar, D., Kulkarni, R., Virkar, R., Krishnan, J., Yadav, A., Baranwal, E., et al. (2024) · Nature Medicine · doi:10.1038/s41591-024-02955-2 · Cited by 66 · see citing works
Yang, B., Lin, Y., Xiong, W., Liu, C., Gao, H., Ho, F. C. S., Zhou, J., Zhang, R., Wong, J. Y., Cheung, J. K., et al. (2023) · The Lancet Regional Health - Western Pacific · doi:10.1016/j.lanwpc.2023.100969 · Cited by 58 · see citing works
Self-citationEstimate of COVID-19 Deaths, China, December 2022–February 2023
Du, Z., Wang, Y., Bai, Y., Wang, L., Cowling, B. J., & Ancel, L. W. (2023) · Emerging infectious diseases · doi:10.3201/eid2910.230585 · Cited by 50 · see citing works
Self-citationReduction in Long COVID Symptoms and Symptom Severity in Vaccinated Compared to Unvaccinated Adults
Maier, H. E., Kowalski-Dobson, T., Eckard, A., Gherasim, C., Manthei, D. M., Meyers, A., Davis, D., Bakker, K. M., Lindsey, K., Chu, Z., et al. (2024) · Open Forum Infectious Diseases · doi:10.1093/ofid/ofae039 · Cited by 20 · see citing works
Darwin review: the evolution of virulence in human pathogens
Gupta, S. (2024) · Proceedings of the Royal Society B Biological Sciences · doi:10.1098/rspb.2023.2043 · Cited by 17 · see citing works
SARS-CoV-2 nonstructural protein 6 from Alpha to Omicron: evolution of a transmembrane protein
Feng, S., O’Brien, A., Chen, D. W., Saeed, M., & Baker, S. C. (2023) · mBio · doi:10.1128/mbio.00688-23 · Cited by 14 · see citing works
SARS-CoV-2 Pneumonia: Advances in Diagnosis and Treatment
Căliman-Sturdza, O. A., Șoldănescu, I., & Gheorghita, R. E. (2025) · Microorganisms · doi:10.3390/microorganisms13081791 · Cited by 12 · see citing works
Nakayama, E. E., & Shioda, T. (2024) · Pathogens · doi:10.3390/pathogens13121109 · Cited by 9 · see citing works
Banete, A., Griffin, B. D., Corredor, J. C., Chien, E., Yip, L., Gunawardena, T. N. A., Nirmalarajah, K., Liang, J., Lee, Y., Leacy, A., et al. (2025) · npj Viruses · doi:10.1038/s44298-025-00092-2 · Cited by 8 · see citing works
Wong, I. O. L., Wong, C., Mak, N., Dai, A., Xiao, J., Wu, P., Ni, M. Y., Liao, Q., & Cowling, B. J. (2024) · Vaccine · doi:10.1016/j.vaccine.2024.04.035 · Cited by 7 · see citing works
Self-citationGrant, R., de Kraker, M. E. A., Buetti, N., Jackson, H., Abbas, M., Sobel, J., Sommerstein, R., Eder, M., Balmelli, C., Troillet, N., et al. (2024) · Clinical Infectious Diseases · doi:10.1093/cid/ciae558 · Cited by 6 · see citing works
The Eye of the Storm: Investigating the Long-Term Cardiovascular Effects of COVID-19 and Variants
Vishwakarma, N., Goud, R. B., Tirupattur, M. P., & Katwa, L. C. (2023) · Cells · doi:10.3390/cells12172154 · Cited by 6 · see citing works
Xin, H., Law, A. H. T., Cheung, J. K., Lin, Y., Wu, P., Li, Z., Cowling, B. J., Yang, W., & Wong, J. Y. (2025) · Journal of Global Health · doi:10.7189/jogh.15.04105 · Cited by 4 · see citing works
Self-citationAntibiotic use in hospitalized patients with COVID-19: a population-based study in Hong Kong
Blais, J. E., Zhang, W., Lin, Y., Chui, C. S. L., Cheng, V. C., Cowling, B. J., & Wu, P. (2023) · Antimicrobial Stewardship & Healthcare Epidemiology · doi:10.1017/ash.2023.485 · Cited by 7 · see citing works
Self-citationYoung, B. R., Ho, F. C. S., Lin, Y., Lau, E. H. Y., Cowling, B. J., Wu, P., & Tsang, T. K. (2023) · The Journal of Infectious Diseases · doi:10.1093/infdis/jiad445 · Cited by 4 · see citing works
Self-citationChiyyeadu, A., Asgedom, G., Bruhn, M., Rocha, C., Schlegel, T. U., Neumann, T., Galla, M., Barbosa, P. V., Hoffmann, M., Ehrhardt, K., et al. (2024) · Clinical Immunology · doi:10.1016/j.clim.2024.109902 · Cited by 3 · see citing works
Association of COVID-19 vaccination with duration of hospitalization in older adults in Hong Kong
Chen, D., Cowling, B. J., Ainslie, K. E. C., Lin, Y., Wong, J. Y., Lau, E. H. Y., Wu, P., & Nealon, J. (2024) · Vaccine · doi:10.1016/j.vaccine.2024.02.074 · Cited by 3 · see citing works
Self-citationLaw, A. H. T., Presanis, A. M., Cheung, J. K., Wu, P., Schooling, C. M., Cowling, B. J., & Wong, J. Y. (2025) · The Lancet Regional Health - Western Pacific · doi:10.1016/j.lanwpc.2025.101571 · Cited by 2 · see citing works
Self-citationMeng, Y., Lin, Y., Xiong, W., Lau, E. H. Y., Ho, F. C. S., Wong, J. Y., Wu, P., Tsang, T. K., Cowling, B. J., & Yang, B. (2024) · The Journal of Infectious Diseases · doi:10.1093/infdis/jiae592 · Cited by 2 · see citing works
Self-citationCoronaviruses: Pandemic SARS-CoV-2
Cowling, B. J., & Wong, S. (2024) · Springer eBooks · doi:10.1007/978-1-4939-9544-8_68-1 · Cited by 2 · see citing works
Self-citationLin, Y., Hay, J. A., Meng, Y. H., Cowling, B. J., & Yang, B. (2025) · PLoS Computational Biology · doi:10.1371/journal.pcbi.1013527 · Cited by 1 · see citing works
Self-citationYoung, B. R., Ho, F. C. S., Lin, Y., Lau, E. H. Y., Wu, P., Cowling, B. J., & Tsang, T. K. (2025) · Journal of Infection and Public Health · doi:10.1016/j.jiph.2025.102972 · Cited by 1 · see citing works
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Law, A. H. T., Presanis, A. M., Cheung, J. K., Wu, P., Schooling, C. M., Cowling, B. J., & Wong, J. Y. (2024) · medRxiv · doi:10.1101/2024.12.12.24318910
Self-citationImmune Driven Pathogen Evolution
Gupta, S. (2024) · Elsevier eBooks · doi:10.1016/b978-0-128-24465-4.00128-9
Wang, C., Li-ping, P., Huang, X., & Tsang, T. K. (2025) · Vaccines · doi:10.3390/vaccines13070747
Optimization of school closures during an Omicron epidemic in Hong Kong: a modelling study
Young, B. R., Ho, F. C. S., Lin, Y., Lau, E. H. Y., Wu, P., Cowling, B. J., & Tsang, T. K. (2025) · Interface Focus · doi:10.1098/rsfs.2025.0016
Self-citationToporowski, G., Mueller-Mai, C. M., Rascher, K., & Wiedemann, J. (2025) · BMC Geriatrics · doi:10.1186/s12877-025-06840-6 · Cited by 1 · see citing works
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Self-citationZhang, Y., Xu, X., Tang, L., Ma, J., & Wang, Y. (2026) · Diagnostics · doi:10.3390/diagnostics16193133
- Authors
- Wong, J. Y., Cheung, J. K., Lin, Y., Bond, H. S., Lau, E. H. Y., Ip, D. K. M., Cowling, B. J., & Wu, P.
- Affiliations
- University of Hong Kong (HK)
- Hong Kong Science and Technology Parks Corporation (HK)
- 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
- Corresponding author
- Cowling, Benjamin J
- Venue
- The Journal of Infectious Diseases
- Publisher
- Oxford University Press (OUP)
- Published
- 2023-06-27
- Volume
- 228
- Issue
- 9
- Pages
- 1231-1239
- ISSN
- 0022-1899 (ISSN-L)
- 1537-6613
- OpenAlex
- W4382182727
- Cited by
- 31
- References
- 30
- Citations by year
- 2026: 3 · 2025: 9 · 2024: 13 · 2023: 6
- FWCI
- 6.43
- Type
- journal article
- Language
- en
- Open access
- green
- dx.doi.org
- Locations
- The Journal of Infectious Diseases (publishedVersion)
- medRxiv (acceptedVersion, cc-by-nd)
- PubMed (publishedVersion)
- Figshare (submittedVersion, cc-by)
- Funders
- Health and Medical Research Fund
- Hong Kong Special Administrative Region (SAR) government (CID-HKU-2-13)
- Collaborative Research Scheme (C7123-20G)
- Research Grants Council
- Hong Kong SAR government
- RGC Senior Research Fellow Scheme (SRFS2021-7S03)
- Hong Kong SAR
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Keywords
- COVID-19 pandemic, SARS-CoV-2, disease severity, case fatality risk, vaccination, epidemic waves, Hong Kong
- MeSH terms
- COVID-19, SARS-CoV-2, Hong Kong, Hospitalization, Humans, Epidemics
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