The preliminary positive case involves a 50-year-old man whose infection was identified through mandatory testing at Hong Kong International Airport, after an airline ground crew member was infected two weeks ago.
He is a porter at the airport who mainly performed duties at the apron, and last went to work on Saturday.
The man received the first dose of the BioNTech vaccine on July 1 and has been asymptomatic, but was found to carry the L452R mutant strain.
Officials said the latest patient doesn’t know the previously infected airport worker.
The building where the man lives at 1-3 Kam Fung Street was cordoned off Saturday at 7.30pm, and residents were required to undergo compulsory testing.
As of midnight, 28 residents had been tested and no confirmed cases were found, authorities said, adding a subsequent enforcement action found that all residents had complied with the testing order.