Impact assessment of non-pharmaceutical interventions against coronavirus disease 2019 and influenza in Hong Kong: an observational study

Prof Benjamin J Cowling, Sheikh Taslim Ali, Tiffany W Y Ng, Tim K Tsang, Julian C M Li, Min Whui Fong, et al

Published: April 17, 2020



A range of public health measures have been implemented to suppress local transmission of coronavirus disease 2019 (COVID-19) in Hong Kong. We examined the effect of these interventions and behavioural changes of the public on the incidence of COVID-19, as well as on influenza virus infections, which might share some aspects of transmission dynamics with COVID-19.


Our study shows that non-pharmaceutical interventions (including border restrictions, quarantine and isolation, distancing, and changes in population behaviour) were associated with reduced transmission of COVID-19 in Hong Kong, and are also likely to have substantially reduced influenza transmission in early February, 2020.


Our findings suggest that the package of public health interventions (including border entry restrictions, quarantine and isolation of cases and contacts, and population behaviour changes, such as social distancing and personal protective measures) that Hong Kong has implemented since late January, 2020, is associated with reduced spread of COVID-19. In the 10 weeks (corresponding to about ten generation times) since the first known individual with COVID-19 in Hong Kong began to show symptoms, there has been little sustained, local transmission of the disease. Our findings strongly suggest that social distancing and population behavioural changes—that have a social and economic impact that is less disruptive than total lockdown—can meaningfully control COVID-19.

The increasing number of imported infections in March poses a challenge to suppression efforts. This increase has occurred at the same time as relaxation of some voluntary avoidance behaviours in the general community. Without a strengthening of social distancing measures, local infections are likely to continue to occur, given that the effective reproduction number is approximately 1 or slightly higher than 1. Travel measures and testing, tracing, and treating efforts are particularly important in maintaining suppression, although these measures will be increasingly difficult to implement as case numbers increase.


The Lancet – DOI: