In early 2020, Hong Kong was one of the first-affected locations outside of mainland China. Timely application of effective public health and social measures as part of a “Dynamic Zero Covid” strategy were able to successfully control a number of surges in daily case numbers in the first two years of the pandemic, keeping the incidence of confirmed cases below 1% of the population. Analysis of transmission dynamics reveals variation over time in epidemiological parameters that might previously have been imagined to remain constant over time, such as serial intervals and overdispersion (superspreading). Two COVID-19 vaccines have available since early 2021, including the BioNTech mRNA vaccine and an inactivated vaccine produced by Sinovac. While local vaccination coverage rose through 2021 into 2022, and mass vaccination provided an opportunity to relax public health measures in other parts of the world, the Hong Kong government continued to follow the “Dynamic Zero Covid” strategy. A large epidemic of Omicron BA.2 occurred in early 2022 resulting in more than 10,000 COVID deaths (>1 per 1000 population), with Hong Kong having the highest COVID-19 mortality rates in 2022 globally. While severity of Omicron has been milder around the world, we find that the intrinsic severity of this strain remains high. We found that both types of COVID vaccines provided very substantial protection against severe COVID, while our community-based studies provide evidence on levels of infections and immunity and allow us to further explore the underlying mechanisms for similarities and differences in vaccine effectiveness including the assessment of correlates of protection.

Bio: Ben Cowling is currently Chair Professor of Epidemiology and head of the Division of Epidemiology and Biostatistics in the School of Public Health at the University of Hong Kong, and co-Director of the WHO Collaborating Centre for Infectious Disease Epidemiology and Control. He conducts research into the epidemiology of respiratory virus infections, with a focus on transmission dynamics and the effectiveness of control measures including vaccination. Since early 2020 he has conducted research on the epidemiology and control of COVID-19 including highly cited publications in NEJM, Science and Nature Medicine. He holds major research grants to study how individual measures of immunity translate to population immunity, and to identify optimal vaccination strategies for influenza and COVID-19. He has authored more than 600 peer-reviewed journal publications to date. He is Editor-in-Chief of Influenza and Other Respiratory Viruses, and an Associate Editor of the journal Emerging Infectious Diseases. In June 2021 he was awarded an MBE by Her Majesty Queen Elizabeth II for services to public health and COVID-19 research.