The Hong Kong SAR Government has implemented timely measures since early 2020 to enhance surveillance and prevention of COVID-19. Five waves of infection have occurred, with the first four waves happening in the pre-vaccination era and totaling around 12,500 cases. The first two waves in 2020 (from January to February and from March to April respectively) were mainly imported cases and small clusters of local transmission, while widespread community outbreaks occurred in the 3rd and 4th waves from July to September 2020 and from November 2020 to March 2021, respectively. Both were controlled through aggressive contact tracing, community testing, and stringent social distancing measures.
Hong Kong managed to maintain a dynamic zero-COVID state from April to December 2021. Most cases during this time were imported cases, with sporadic spillovers that did not result in sustained spread. Imported cases of Omicron variant have been detected since mid-November 2021, sparking the 5th wave in late December 2021.
The 5th wave has recorded around 2.86 million cases (as of January 29, 2023) with three periods of upsurge (February to March predominated by BA.2; August to September predominated by BA.5; and November to December predominated by BA.5). Airborne transmission of Omicron was demonstrated in outbreaks in restaurants and designated quarantine hotels, making containment difficult through contact tracing and social distancing measures. Large outbreaks have occurred in residential care institutions (RCH) with a median attack rate of around 85%. Vertical transmissions in high-rise residential buildings were also common.
The case fatality rate (CFR) among the elderly was much higher than in younger age groups, with elderly aged 60 years or older constituting 25% of cases but 95% of deaths. Among the 13115 fatal cases recorded in 5th wave, 93% had chronic diseases and 47% were RCH residents. The overall CFR decreased from 1.68% during the 1st to 4th waves to 0.45% in the 5th wave. Cases in the 5th wave who had received at least 3 doses of vaccination had a CFR of 0.16% as compared to 0.80% among cases with 2 doses or less. The vaccination coverage has been boosted up through various measures and extensive interdepartmental and multisectoral efforts. With gradual increase in vaccination coverage, hybrid immunity, and the more extensive use of oral antiviral treatment in community settings, the CFR in the 5th wave dropped from 0.78% (2.85% among unvaccinated) between January and May 2022 to 0.23% (0.67% among unvaccinated) between June 2022 and January 2023.
The Centre for Health Protection will continue to closely monitor the evolving COVID-19 situation through established surveillance systems, including genetic characterization and sewage surveillance.
