The Centre for Health Protection today said that among the 5,609 COVID-19 cases reported between December 1 last year and June 30 this year, only 393 were variant cases, most of which were imported.

The 393 cases included 291 variants of concern, 73 variants of interest and 29 alerts for further monitoring.

This epidemiological review showed that, unlike some places which saw surges of variant cases following their introduction, neither widespread community outbreak nor sustained local transmission of COVID variants was observed in Hong Kong, the centre noted.

Only three clusters involving local transmission of COVID-19 variants were identified. While two clusters were linked to imported cases, the remaining cluster’s infection source was unknown.

Additionally, since nearly half of the patients in the three clusters were identified during quarantine in a quarantine centre, further community spread was successfully contained.

The centre stressed that such success was found to be attributed to the strengthening of public health control measures against variants at various stages, including risk-stratified quarantine and testing requirements for inbound travellers, banning of flights from extremely high-risk areas, enhanced contact tracing and quarantine to 21 days, extensive community testing and increased laboratory surveillance.

The use of whole genome sequencing by its Public Health Laboratory Services Branch (PHLSB) was pivotal to identifying the sources of the clusters with local transmission, the centre emphasised.

It also pointed out that the PHLSB was the first institute in the world to upload the whole genome sequences of the Omicron variant to the international genomic database GISAID (global initiative on sharing all influenza data) on November 22, contributing to the global surveillance of variant strains.

Findings of the centre’s epidemiological review and information on public health control measures have been released as a preprint pending formal publication in an official journal of the International Society for Infectious Diseases.