A research team at City University of Hong Kong (CityU) estimated in mid-January, i.e. before the recent outbreak of the fifth wave, that if social mobility decreases by around 25% when compared to the level during the Christmas and New Year holidays, a fifth wave will cause around 250,000 infected cases, which is similar to the current pandemic trend in Hong Kong.

Dr Sean Yuan Hsiang-yu, Assistant Professor in the Department of Biomedical Sciences at CityU, and his team developed a mathematical model earlier that combined age-specific susceptibility to COVID-19 infections and social contact data, among others.

Dr Yuan said the current rise in the case number of the fifth wave was largely due to frequent contact during the Chinese New Year holiday and the reduction in contact tracing efficiency due to the increase in the number of infected people. When confirmation delay occurs, the number of confirmed cases is likely to increase exponentially.

Dr Yuan’s research team collaborated with the JC School of Public Health and Primary Care at the Chinese University of Hong Kong; Department of Social and Behavioural Sciences at CityU; Sungkyunkwan University, Seoul; and the Faculty of Medicine at Imperial College London.

The CityU study utilises an age-stratified mathematical model that takes into account age-specific susceptibility to COVID-19 infection, the effectiveness of the two COVID-19 vaccines in Hong Kong, mobility data, social contact data in the community, contact tracing efficacy similar to that in the fourth wave, and the severity rate of Omicron being half that of Delta.

The aim was to simulate the number of infections that may be caused by the fifth wave under different intervention policies: assuming (i) 65% of the population has received at least one dose of the vaccine, (ii) vaccine effectiveness against infection is 50% (Sinovac) and 70% (BioNTech), (iii) the basic reproduction number (R0) for Omicron is 8 (when the entire population is susceptible, not vaccinated or there is no exercising of social distancing measures), and (iv) antibodies wane across time.

The team estimated on 7 January that, after the government introduces tightened social distancing measures, if social mobility decreases by 25% when compared to the level during the Christmas and New Year holidays, the fifth wave will cause around 250,000 infections, which is similar to the current pandemic trend in Hong Kong.

“According to the current situation, if social distancing measures are not efficient, we expect the fifth wave to peak at the end of February or in March, and the number of infected cases will gradually decline until the vaccination coverage for the third dose reaches a certain level,” Dr Yuan said.

He suggested that:

1. the government introduces a medium-scale rapid testing scheme for local residents in high-risk areas such as Sham Shui Po and Kwai Chung so as to identify as many potentially infected people as possible within one to two weeks, and then conduct centralised tracking and isolation. This approach is more effective at tracking than implementing rapid testing for the entire population to block the spread of COVID-19;
2. the current 6 months interval of the third dose should be shortened to 3 months to increase the coverage of the booster shot as soon as possible;
3. to avoid vertical infection inside a building during mandatory screening, public spaces can be sterilised using ultraviolet equipment.

Dr Yuan’s application to carry out research in the field of public health at CityU was approved by President Way Kuo of CityU and an interview panel following a global recruitment drive by the Jockey Club College of Veterinary Medicine and Life Sciences, which was established in 2018.

Before joining CityU, Dr Yuan was engaged in human genomic medicine research at the Institute of Biomedical Sciences, Academia Sinica, Taiwan, from 2003 to 2006. He then pursued a PhD in Biocomputing at Duke University, US. He worked on predictive models for infectious diseases in the Department of Infectious Disease Epidemiology at Imperial College London in 2013, and he was engaged in dengue research at the National Health Research Institutes in Taiwan in 2017.