Comparison of control and transmission of COVID-19 across epidemic waves in Hong Kong: an observational study (preprint)

Background: Hong Kong contained COVID-19 for two years, but experienced a large epidemic of Omicron BA.2 in early 2022 and endemic transmission of Omicron subvariants thereafter. Methods: We examined the use and impact of pandemic controls in Hong Kong by analysing data on more than 1.7 million confirmed COVID-19 cases and characterizing non-pharmaceutical and pharmaceutical interventions implemented from January 2020 through to 30 December 2022. We estimated the daily effective reproductive number (Rt) to track changes in transmissibility and effectiveness of community-based measures against infection over time. We examined the temporal changes of pharmaceutical interventions, mortality rate and case-fatality risks (CFRs), particularly among older adults. Findings: Hong Kong experienced four local epidemic waves predominated by the ancestral strain in 2020 and early 2021 and prevented multiple SARS-CoV-2 variants from spreading in the community before 2022. Strict travel-related, case-based, and community-based measures were increasingly tightened in Hong Kong over the first two years of the pandemic. However, even very stringent measures were unable to contain the spread of Omicron BA.2 in Hong Kong. Despite high overall vaccination uptake (>70% with at least two doses), high mortality was observed during the Omicron BA.2 wave due to lower vaccine coverage (42%) among adults [≥]65 years of age. Increases in antiviral usage and vaccination uptake over time through 2022 was associated with decreased case fatality risks. Interpretation: Integrated strict measures were able to reduce importation risks and interrupt local transmission to contain COVID-19 transmission and disease burden while awaiting vaccine development and rollout. Increasing coverage of pharmaceutical interventions among high-risk groups reduced infection-related mortality and mitigated the adverse health impact of the pandemic.

Viral shedding among symptomatic COVID-19 cases infected with the ancestral strain and Omicron BA.2 (preprint)

Assessment of viral kinetics of SARS-CoV-2 may inform host immune responses to and transmission potential of the virus. We analyzed longitudinal data of RT-PCR tests conducted for symptomatic COVID-19 patients at confirmation and during hospital isolation in Hong Kong during three major epidemic waves, and modeled the temporal trajectories of viral burden in these patients. Our analysis demonstrated that a longer duration of viral shedding appeared in more severe and older cases. Vaccinated individuals with a breakthrough infection of Omicron BA.2 exhibited a lower viral burden than non-vaccinated Omicron cases in early days following onset and a shorter duration of viral shedding particularly in more recently vaccinated patients. The viral kinetics characterized in our study provided insight into further studies on host immune responses to SARS-CoV-2 infection, prognosis of COVID-19 patients as well as possible protective mechanisms of vaccination against infection and severe outcomes.

Residential clustering of COVID-19 cases and efficiency of building-wide compulsory testing notices as a transmission control measure in Hong Kong (preprint)

Background: Despite relatively few reports of residential case clusters of COVID-19, building-wide compulsory testing notices on residential apartment blocks are frequently applied in Hong Kong with the aim of identifying cases and reducing transmission. Methods: We aimed to describe the frequency of residential case clusters and the efficiency of compulsory testing notices in identifying cases. The residences of locally infected COVID-19 cases in Hong Kong were grouped to quantify the number of cases per residence. Buildings targeted in compulsory testing notices were matched with the residence of cases to estimate the number of cases identified. Results: We found that most of the residential buildings (4246/7688, 55.2%) with a confirmed COVID-19 case had only one reported case. In the fourth and the fifth epidemic wave in Hong Kong, we estimated that compulsory testing notices detected 29 cases (95% confidence interval: 26, 32) and 46 cases (44, 48) from every 100 buildings tested (each with hundreds of residents), respectively. Approximately 13% of the daily reported cases were identified through compulsory testing notices. Conclusions: Compulsory testing notices can be an essential method when attempting to maintain local elimination (zero covid) and most impactful early in an epidemic when the benefit remains of stemming a new wave. Compulsory testing therefore appears to be a relatively inefficient control measure in response to sustained community transmission in the community.

Epidemiology of infections with SARS-CoV-2 Omicron BA.2 variant in Hong Kong, January-March 2022 (preprint)

Hong Kong reported 12,631 confirmed COVID-19 cases and 213 deaths in the first two years of the pandemic but experienced a major wave predominantly of Omicron BA.2.2 in early 2022 with over 1.1 million reported SARS-CoV-2 infections and more than 7900 deaths. Our data indicated a shorter incubation period, serial interval, and generation time of infections with Omicron than other SARS-CoV-2 variants. Omicron BA.2.2 cases without a complete primary vaccination series appeared to face a similar fatality risk to those infected in earlier waves with the ancestral strain.

Time-varying transmission heterogeneity of SARS and COVID-19 in Hong Kong (preprint)

Transmission heterogeneity is a notable feature of the severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19) epidemics, though previous efforts to estimate how heterogeneity changes over time are limited. Using contact tracing data, we compared the epidemiology of SARS and COVID-19 infection in Hong Kong in 2003 and 2020-21 and estimated time-varying transmission heterogeneity (kt) by fitting negative binomial models to offspring distributions generated across variable observation windows. kt fluctuated over time for both COVID-19 and SARS on a continuous scale though SARS exhibited significantly greater (p < 0.001) heterogeneity compared to COVID-19 overall and in-time. For COVID-19, kt declined over time and was significantly associated with increasingly stringent non-pharmaceutical interventions though similar evidence for SARS was inconclusive. Underdetection of sporadic COVID-19 cases led to a moderate overestimation of kt, indicating COVID-19 heterogeneity of could be greater than observed. Time-varying or real-time estimates of transmission heterogeneity could become a critical indicator for epidemic intelligence in the future.

Teaching psychology online

Although this e-book was proposed prior to the emergence of COVID-19, the pandemic pushed many more psychology faculty and students to participate in the exciting and rewarding enterprise of online learning. This has provided critical opportunities to learn how contemporary psychology faculty instruct their students in online courses, with many illustrative examples offered in this volume. The first of its kind, this e-book focuses exclusively on how faculty use different delivery formats, from fully asynchronous courses to those with required synchronous components, to teach psychology to diverse students matriculating in a range of academic programs and institutions. The majority of chapters focus on the intentional design and delivery of online psychology courses, though some chapters also offer interesting insights into how colleagues adapted their established on-ground psychology courses for remote delivery subsequent to the pandemic. Each chapter is connected to online learning and teaching research, scholarship of teaching and learning, or both, and offers an overview of the learning objectives, assigned materials, and class activities and assignments characterizing authors' classes. (PsycInfo Database Record (c) 2021 APA, all rights reserved)

Incorporating temporal distribution of population-level viral load enables real-time estimation of COVID-19 transmissibility (preprint)

Many locations around the world have used real-time estimates of the time-varying effective reproductive number (\({R}_{t}\)) of COVID-19 to provide evidence of transmission intensity to inform control strategies. Estimates of \({R}_{t}\) are typically based on statistical models applied to case counts and typically suffer lags of more than a week because of the incubation period and reporting delays. Noting that viral loads tend to decline over time since illness onset, analysis of the distribution of viral loads among confirmed cases can provide insights into epidemic trajectory. Here, we analyzed viral load data on confirmed cases during two local epidemics in Hong Kong, identifying a strong correlation between temporal changes in the distribution of viral loads (measured by cycle threshold values) and estimates of \({R}_{t}\) based on case counts. We demonstrate that cycle threshold values could be used to improve real-time \({R}_{t}\) estimation, enabling more timely tracking of epidemic dynamics.

Universal Community Nucleic Acid Testing for COVID-19 in Hong Kong Reveals Insights into Transmission Dynamics (preprint)

Background: Testing of an entire community has been used as an approach to control COVID-19. In Hong Kong, a universal community testing programme (UCTP) was implemented at the fadeout phase of a community epidemic in July to September 2020, to determine the prevalence of unrecognised cases and limit any remaining transmission chains. We described the utility of the UCTP in finding unrecognised cases, and analysed data from the UCTP and other sources to characterise transmission dynamics.Methods: We described the characteristics of people participating in the UCTP, and compared the clinical and epidemiological characteristics of COVID-19 cases detected by the UCTP versus those detected by clinical diagnosis and public health surveillance. We developed a Bayesian model to estimate the age-specific incidence of infection and the proportion of cases detected by clinical diagnosis and public health surveillance.Findings: 1.77 million people, 24% of the Hong Kong population, participated in the UCTP from 1 to 14 September 2020. The UCTP identified 32 new infections (1.8 per 100,000 samples tested), consisting of 29% of all local cases reported during the two-week UCTP period. Compared with the existing clinical diagnosis and public health surveillance, the UCTP detected a higher proportion of sporadic cases (62% versus 27%, p <0.01) and identified 6 (out of 18) additional transmission chains during that period. We estimated that 27% (95% credible interval: 22%, 34%) of all infections were detected by the existing clinical diagnosis and public health surveillance in the third wave.Interpretation: We reported empirical evidence of the utility of population-wide COVID-19 testing in detecting unrecognised infections and transmission chains. Around three quarters of infections have not been identified through existing surveillance approaches including contact tracing.Funding Statement: This project was supported by the Health and Medical Research Fund, Food and Health Bureau, Government of the Hong Kong Special Administrative Region (grant no. COVID190118).Declaration of Interests: BJC consults for Roche, Sanofi Pasteur, GSK and Moderna. The authors report no other potential conflicts of interest.Ethics Approval Statement: Our project was approved by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (HKU/HA HKW IRB).

Clustering and superspreading potential of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in Hong Kong (preprint)

Superspreading events have characterised previous epidemics of severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) infections. Using contact tracing data, we identified and characterized SARS-CoV-2 clusters in Hong Kong. Given a superspreading threshold of 6-8 secondary cases, we identified 5-7 probable superspreading events and evidence of substantial overdispersion in transmissibility, and estimated that 20% of cases were responsible for 80% of local transmission. Among terminal cluster cases, 27% (45/167) ended in quarantine. Social exposures produced a greater number of secondary cases compared to family or work exposures (p<0.001) while delays between symptom onset and isolation did not reliably predict the number of individual secondary cases or resulting cluster sizes. Public health authorities should focus on rapid tracing and quarantine of contacts, along with physical distancing to prevent superspreading events in high-risk social environments.