Estimating the Severity of Covid-19 Cases in Hong Kong, from January 2020 to January 2023

Abstract

Background

Severity of COVID-19 has been difficult to measure in the face of rapidly evolving virus variants and changing data. Accurate assessments of the severity of COVID-19 are needed to characterize the health burden of the disease and evaluate the public health response. Here we used COVID-19 patient data from Hong Kong to quantify the impact of COVID-19 during the six waves of activity up to January 2023 by estimating the fatality risks under the severity pyramid approach.

 

Methods

The severity pyramid structure was adopted to estimate severity measured by the case-fatality risk, estimating this via the case-hospitalization risk multiplied by the hospitalization-fatality risk. Surveillance data of different levels in the severity pyramid were collected from Hospital Authority and Centre for Health Protection of Hong Kong. Bayesian analysis was carried out to obtain estimates of severity and associated uncertainties. We investigated the impact of hospitalization definition and severity criteria on severity estimation.

 

Results

Wave-specific estimates show that severity has generally declined over time in terms of case hospitalization risk and case fatality risk, while hospitalization fatality risk peaked during a large community epidemic predominated by Omicron BA.2. A consistent increasing trend with age was observed across all metrics, with the highest risks occurring in adults aged 80 years or older. Case fatality risk decreased substantially with the total doses of vaccine that an individual had received especially in the elderly. During the peak of the Omicron wave, case fatality risk of those aged ≥80 years was estimated to be 12.64% (95% CrI: 12.28%-13.00%) in unvaccinated individuals and 1.18% (95% CrI: 0.83%-1.64%) in persons with a booster dose.

 

Implications

This study assessed COVID-19 case fatality risks using a pyramid approach with combined data from several levels of the pyramid, which might be able to improve severity assessment. We also studied the risk factors of mortality to inform future public health policies.

Note: This conference abstract was presented at the 9th International Conference on Infectious Disease Dynamics organized by the journal Epidemics. This abstract has not been screened by SSRN for potential for public harm and should not be used to inform any clinical decision making. No competing interests or funding statements have been declared.