Lessons Learnt From Hong Kong's Successful Strategy in Combatting Two Outbreak Waves of COVID-19 Pandemic: A Retrospective Cohort Study

Abstract

Background: Hong Kong has been fighting the coronavirus disease 2019 (COVID-19) for over a year, experiencing four major outbreak waves, and how the varying public health measures implemented by the Government at different stages impacted the epidemics remains unknown. Evaluating the role of diverse public health measures played across the third and fourth outbreak waves dominated by local transmissions in Hong Kong, would guide other regions in designing intervention policies. Methods: We collected individual data from the official website of the Department of Health of Hong Kong Government for period from July 5, 2020 through May 6, 2021, covering the third and fourth outbreak waves. We divided the whole period into six sub-periods according to the social distancing measures’ staged characteristics. The third wave experienced three periods: July 5 – July 28, July 29 – August 27, and August 28 – November 15 of year 2020. The fourth wave had three periods: November 16 – December 9, 2020, December 10, 2020 – February 17, 2021, and February 18 – May 6, 2021. We estimated daily infected cases per day per million people across age, sex, infection source and geographical districts. We used smoothing splines to evaluate the growth velocity and acceleration. We also compared the duration from symptom onset to report for each wave. Findings: We studied 10,540 laboratory-confirmed cases, among which 4,987 (47.3%) were male. The median age of patients was 45 years (31-60), with the most cases aged 40-59 and 20-39. Daily infection rate achieved peaks in the first sub-period of either wave, then declined in the second sub-period, and finally decreased to a small value in the last sub-period. The fourth wave had significantly decreased 1.2 (0.9-1.4) days for duration of symptom onset to report compared to the third wave. Interpretation: Our results suggested that the more aggressive public health measures including compulsory testing, partial lockdown and intensive contact tracing implemented during the fourth wave, were more effective in controlling the epidemic compared with the third outbreak wave. The findings may enlighten other regions in combating the COVID-19. Funding Information: NA. Declaration of Interests: We declare no competing interests.