Authorities acted after a confirmed case, and two preliminary positives, were detected in people who had returned from overseas. Two of them were carrying the L452R mutation, including the confirmed case in Wan Chai. The mutation is found in the very contagious delta variant but is not unique to it.
Officials said the Taikoo cases involved a 13-year-old girl and her 11-year-old brother, who had arrived from Saudi Arabia last Friday. They had been exempt from hotel quarantine and self-isolated.
Their airport Covid tests were negative but deep throat saliva samples, submitted a few days later, came back positive.
The Wan Chai case involves a 39-year-old man, who returned from France on Sunday.
Officials believe all three were infected overseas.