Contribution of low population immunity to the severe Omicron BA.2 outbreak in Hong Kong

Lin-Lei Chen, Syed Muhammad Umer Abdullah, Wan-Mui Chan, Brian Pui-Chun Chan, Jonathan Daniel Ip, Allen Wing-Ho Chu, Lu Lu, Xiaojuan Zhang, Yan Zhao, Vivien Wai-Man Chuang, Albert Ka-Wing Au, Vincent Chi-Chung Cheng, Siddharth Sridhar, Kwok-Yung Yuen, Ivan Fan-Ngai Hung, Kwok-Hung Chan and Kelvin Kai-Wang To ()
Additional contact information
Lin-Lei Chen: The University of Hong Kong
Syed Muhammad Umer Abdullah: The University of Hong Kong
Wan-Mui Chan: The University of Hong Kong
Brian Pui-Chun Chan: The University of Hong Kong
Jonathan Daniel Ip: The University of Hong Kong
Allen Wing-Ho Chu: The University of Hong Kong
Lu Lu: The University of Hong Kong
Xiaojuan Zhang: The University of Hong Kong
Yan Zhao: The University of Hong Kong
Vivien Wai-Man Chuang: Quality and Safety Division, Hospital Authority
Albert Ka-Wing Au: Centre for Health Protection, Department of Health
Vincent Chi-Chung Cheng: The University of Hong Kong
Siddharth Sridhar: The University of Hong Kong
Kwok-Yung Yuen: The University of Hong Kong
Ivan Fan-Ngai Hung: The University of Hong Kong
Kwok-Hung Chan: The University of Hong Kong
Kelvin Kai-Wang To: The University of Hong Kong

Nature Communications, 2022, vol. 13, issue 1, 1-10

Abstract: 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.

Date: 2022
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DOI: 10.1038/s41467-022-31395-0

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