Hong Kong appeared to have averted a major COVID-19 outbreak up to March 31, 2020, by adopting far less drastic control measures than most other countries, with a combination of border entry restrictions, quarantine and isolation of cases and contacts, together with some degree of social distancing, according to a new study conducted by researchers at the WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, LKS Faculty of Medicine of the University of Hong Kong (HKUMed). The findings are now published in The Lancet Public Health journal [link to publication].

As of March 31, 2020, Hong Kong had 715 confirmed COVID-19 cases including 94 asymptomatic infections, and 4 deaths. The control measures implemented in Hong Kong since late January included intense surveillance for infections, not only for incoming travellers, but also in the local community, with around 400 outpatients and 600 inpatients tested every day in early March. Extensive efforts were also made to track down and quarantine all close contacts an infected person had seen two days before becoming ill, and holiday camps and newly built housing estates were repurposed into quarantine facilities. Additionally, anyone crossing the border from mainland China, as well as travellers from infected countries, were required to undergo 14 days of mandatory quarantine at home or in designated facilities. The government also deployed measures to encourage social distancing including flexible working arrangements and school closures, and many large-scale events were cancelled.

“By quickly implementing public health measures, Hong Kong has demonstrated that COVID-19 transmission can be effectively contained without resorting to the highly disruptive complete lockdown adopted by mainland China, the USA, and Western European countries,” said Professor Benjamin Cowling, Division Head of Epidemiology and Biostatistics, School of Public Health, HKUMed, and Co-Director of the WHO Collaborating Centre for Infectious Disease Epidemiology and Control, who led the research. “Other governments can learn from the success of Hong Kong. If these measures and population responses can be sustained, while avoiding fatigue among the general population, they could substantially lessen the impact of a local COVID-19 epidemic.”

In the study, researchers analysed data on laboratory-confirmed COVID-19 cases in Hong Kong between late January and 31 March, 2020, to estimate the daily rate at which the virus is transmitted—known as the daily effective reproductive number (Rt) for COVID-19, and changes in transmissibility over time1. To examine whether control measures have been associated with reducing silent transmission of COVID-19 (i.e. transmission in the community from people never diagnosed), researchers also analysed influenza surveillance data in outpatients of all ages and influenza hospitalisations in children, as a proxy for changes in COVID-19 transmission—assuming a similar mode and efficiency of spread between influenza and COVID-19.

The researchers also conducted three cross-sectional telephone surveys among the general adult population (aged 18 and older) of Hong Kong to assess attitudes to COVID-19 and changes in behaviours from January to March. Results show that individual behaviours in the Hong Kong population have changed in response to COVID-19. In the most recent survey in March, 85% of respondents reported avoiding crowded places, and 99% reported wearing face masks when leaving home—up from 75% and 61% respectively from the first survey in January. This compares to reported face mask use of around 79% in similar surveys during the SARS outbreak in 2003, and 10% during the influenza A (H1N1) pandemic in 2009. These changes in behaviour indicate the level of concern among the population about COVID-19.

The analyses suggest that influenza transmission declined substantially after the implementation of physical distancing measures and changes in population behaviours in late January—with a 44% reduction in the influenza transmission rate in February, from an estimated average Rt of 1.28 in the two weeks before the start of school closures to 0.72 during the closure weeks. This is much greater than the 10–15% reduction in influenza transmission associated with school closures during the 2009 influenza (H1N1) pandemic, and the 16% decline in transmission of influenza B during the 2017–18 winter in Hong Kong.

“The speed of decline in influenza activity in 2020 was quicker than in previous years when only school closures were implemented, suggesting that other social distancing measures and avoidance behaviours have had a substantial additional impact on influenza transmission,” said co-author Dr Peng Wu, Assistant Professor, School of Public Health, HKUMed. “As both influenza and COVID-19 are directly transmissible respiratory pathogens with similar viral shedding dynamics, it’s likely that these control measures have also reduced COVID-19 transmission in the community.”

She added, “As one of the most heavily affected epicentres during the SARS epidemic in 2003, Hong Kong is better equipped to contend with an outbreak of COVID-19 than many other countries. Improved testing and hospital capacity to handle novel respiratory pathogens, and a population acutely aware of the need to improve personal hygiene and maintain physical distancing, put them in good stead.”