Contribution of low population immunity to the severe Omicron BA.2 outbreak in Hong Kong
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Abstract
Monitoring population protective immunity against SARS-CoV-2 variants is critical for risk assessment. We hypothesize that Hong Kong’s explosive Omicron BA.2 outbreak in early 2022 could be explained by low herd immunity. Our seroprevalence study using sera collected from January to December 2021 shows a very low prevalence of neutralizing antibodies (NAb) against ancestral virus among older adults. The age group-specific prevalence of NAb generally correlates with the vaccination uptake rate, but older adults have a much lower NAb seropositive rate than vaccination uptake rate. For all age groups, the seroprevalence of NAb against Omicron variant is much lower than that against the ancestral virus. Our study suggests that this BA.2 outbreak and the exceptionally high case-fatality rate in the ≥80 year-old age group (9.2%) could be attributed to the lack of protective immunity in the population, especially among the vulnerable older adults, and that ongoing sero-surveillance is essential.
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The VE estimates against Omicron BA.2 infection are robust against the limitations of test-negative designs because Hong Kong had negligible infection-derived immunity before January 2022 and infection histories were individually inferred from serology.
“Our estimates of VE against Omicron BA.2 infection are robust against the abovementioned limitations because Hong Kong had negligible infection-derived immunity against any SARS-CoV-2 before to January 2022, and the infection histories of our subjects were individually inferred based on their serological measurements (irrespective of history of symptoms, case confirmation or contact)19.”
From Real-world COVID-19 vaccine effectiveness against the Omicron BA.2 variant in a SARS-CoV-2 infection-naive population (2023) · cites this paper as [19]
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Experimental — accuracy not yet measuredIn some countries, BA.2 was responsible for a greater share of cases, hospitalizations and deaths during the Omicron wave.
“in some countries, BA.2 was responsible for a greater share of cases, hospitalizations and deaths during the Omicron wave2–4.”
From Emergence of SARS-CoV-2 Omicron lineages BA.4 and BA.5 in South Africa (2022) · cites this paper as [4]
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- Authors
- Chen, L.-L., Abdullah, S. M. U., Chan, W.-M., Chan, B. P.-C., Ip, J. D., Chu, A. W.-H., Lu, L., Zhang, X., Zhao, Y., Chuang, V. W.-M., Au, A. K.-W., Cheng, V. C.-C., Sridhar, S., Yuen, K.-Y., Hung, I. F.-N., Chan, K.-H., & To, K. K.-W.
- Affiliations
- University of Hong Kong (HK)
- Hospital Authority (HK)
- Department of Health (CN)
- Queen Mary Hospital (CN)
- University of Hong Kong - Shenzhen Hospital (CN)
- Corresponding author
- To, Kelvin Kai-Wang
- ORCID
- Venue
- Nature Communications
- Published
- 2022-06-24
- Volume
- 13
- Issue
- 1
- Pages
- 3618-3618
- ISSN
- 2041-1723 (ISSN-L)
- PMC
- PMC9232516
- OpenAlex
- W4283392031
- Cited by
- 72
- References
- 49
- Citations by year
- 2026: 6 · 2025: 6 · 2024: 17 · 2023: 22 · 2022: 21
- FWCI
- 8.05
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- Nature Communications (publishedVersion, cc-by)
- Research Square (acceptedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- RePEc: Research Papers in Economics (submittedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Funders
- Osteogenesis Imperfecta Foundation
- Food and Health Bureau (COVID190124)
- Hui Hoy and Chow Sin Lan Charity Fund
- Hong Kong Government
- Health and Medical Research Fund (COVID190124)
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Health Sciences › Medicine › Infectious Diseases › COVID-19 Clinical Research Studies
- Keywords
- Omicron BA.2, SARS-CoV-2, herd immunity, neutralizing antibodies, seroprevalence, older adults, COVID-19 vaccine uptake, case fatality rate, sero-surveillance, age-specific immunity
- MeSH terms
- COVID-19, SARS-CoV-2, Aged, Aged, 80 and over, Antibodies, Viral, Disease Outbreaks, Hong Kong, Humans, Seroepidemiologic Studies, Antibodies, Neutralizing
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