The 75-year-old had both doses of the Pfizer-BioNTech vaccine in the US, receiving the shots in April and May. He was asymptomatic when he arrived in Hong Kong on Friday.
The 25-year-old is a domestic helper who flew into the city on Wednesday.
She was also asymptomatic and tested positive for Covid-19 on the third day of her quarantine at the Silka Seaview Hotel in Yau Ma Tei
Both patients were positive for the L452R mutation.
Over the past fortnight, Hong Kong has recorded 17 cases – 16 imported and one imported-related.
Hong Kong’s tally of confirmed coronavirus cases stands at 11,958.