Abstract

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In early 2020, Hong Kong was one of the first-affected locations outside of mainland China. However, in the first two years of the pandemic timely public health measures as part of a “Dynamic Zero Covid” strategy were able to successfully control a number of surges in daily case numbers, restricting confirmed cases to well below 1% of the population. Epidemiological analyses have improved our understanding of disease dynamics and the impact of control measures. For example, one of the most interesting phenomena in transmission has been “super-spreading”, in which we have determined that a minority of infections are responsible for a majority of transmission events.

In recent work, we have been examining how and why superspreading dynamics might vary over time. While mass vaccination provides a pathway back to a new normal in most parts of the world, the Hong Kong government has followed the strategy in mainland China of continuing “Dynamic Zero Covid” even when vaccine coverage reaches a high level. Our community studies provide evidence on levels of infections and immunity, and allow us to contrast the difference in effectiveness of the inactivated vaccine (Sinovac) and the mRNA vaccine (BioNTech/Fosun Pharma/Pfizer) being used in Hong Kong