The Centre for Health Protection (CHP) on Sunday said two of the patients – a 19-year-old girl from the US and a 41-year-old woman from Cambodia – were fully inoculated with the BioNTech and Sinovac jabs respectively.
The 41-year-old Cambodian woman was also found to be carrying the N501Y and E484K variant strain.
There were also around five preliminary positive cases.
Officials urged people, including those who’re fully vaccinated, to continue avoiding non-essential travel.
“The global situation of Covid-19 infection remains severe and there is a continuous increase in the number of cases involving mutant strains that carry higher transmissibility, and there are also reports of breakthrough infections in some vaccinated individuals,” a CHP spokesman said.
Meanwhile, health authorities said they have also been notified of a case in the UK involving a woman who had lived in Lok Yuen in Kowloon City.
People who have visited the building have been ordered to get tested.
There have been no local cases in the past month, and the city has so far reported 11,987 cases in total.