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

TLDR

Hong Kong implemented a range of public health measures to suppress local COVID‑19 transmission. The study examined how these interventions and public behavioural changes affected COVID‑19 incidence and influenza virus infections. Researchers estimated daily effective reproduction numbers for COVID‑19 and influenza A H1N1 and surveyed public attitudes through three telephone surveys to assess changes in transmissibility over time. Interventions were associated with sustained COVID‑19 transmissibility near 1 and a 44 % reduction in community influenza transmissibility (Rt 1.28 to 0.72) and a 33 % reduction in pediatric hospitalisation transmissibility (Rt 1.10 to 0.73). Survey respondents reported high mask‑wearing (74.5–98.8 %) and avoidance of crowds (61.3–90.2 %), and the study was funded by the Health and Medical Research Fund, Hong Kong.

Abstract

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.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.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.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.Health and Medical Research Fund, Hong Kong.