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

Lancet Public Health. 2020 May;5(5):e279-e288. doi: 10.1016/S2468-2667(20)30090-6. Epub 2020 Apr 17.


Background: 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.

Methods: We analysed data on laboratory-confirmed COVID-19 cases, influenza surveillance data in outpatients of all ages, and influenza hospitalisations in children. We estimated the daily effective reproduction number (Rt) for COVID-19 and influenza A H1N1 to estimate changes in transmissibility over time. Attitudes towards COVID-19 and changes in population behaviours were reviewed through three telephone surveys done on Jan 20-23, Feb 11-14, and March 10-13, 2020.

Findings: COVID-19 transmissibility measured by Rt has remained at approximately 1 for 8 weeks in Hong Kong. Influenza transmission declined substantially after the implementation of social distancing measures and changes in population behaviours in late January, with a 44% (95% CI 34-53%) reduction in transmissibility in the community, from an estimated Rt of 1·28 (95% CI 1·26-1·30) before the start of the school closures to 0·72 (0·70-0·74) during the closure weeks. Similarly, a 33% (24-43%) reduction in transmissibility was seen based on paediatric hospitalisation rates, from an Rt of 1·10 (1·06-1·12) before the start of the school closures to 0·73 (0·68-0·77) after school closures. Among respondents to the surveys, 74·5%, 97·5%, and 98·8% reported wearing masks when going out, and 61·3%, 90·2%, and 85·1% reported avoiding crowded places in surveys 1 (n=1008), 2 (n=1000), and 3 (n=1005), respectively.

Interpretation: 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.

Funding: Health and Medical Research Fund, Hong Kong.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Betacoronavirus / isolation & purification
  • COVID-19
  • Child
  • Coronavirus Infections / diagnosis
  • Coronavirus Infections / epidemiology
  • Coronavirus Infections / prevention & control*
  • Cross-Sectional Studies
  • Health Knowledge, Attitudes, Practice
  • Hong Kong / epidemiology
  • Hospitalization / statistics & numerical data
  • Humans
  • Incidence
  • Influenza A Virus, H1N1 Subtype*
  • Influenza, Human / epidemiology
  • Influenza, Human / prevention & control*
  • Influenza, Human / therapy
  • Pandemics / prevention & control*
  • Pneumonia, Viral / diagnosis
  • Pneumonia, Viral / epidemiology
  • Pneumonia, Viral / prevention & control*
  • Risk Assessment
  • SARS-CoV-2