HONG KONG - Hong Kong reported 11 new COVID-19 infections on Friday, including one untraceable local case with a mutant strain, bringing the city's overall tally to 11,938.

The local case involved a 41-year-old hotel cleaner who lives with three family members at Port Centre in Aberdeen. Test results showed she was carrying the highly transmissible L452R variant strain, prompting the authorities to designate on Thursday evening the building she lives in as a “restricted area” where people are required to undergo COVID-19 testing.

Around 580 residents there have been tested and no one was found with the virus, Chuang Shuk-kwan, head of the Centre for Health Protection’s communicable disease branch, said at a press briefing Friday.

The woman remained asymptomatic and tested negative for the coronavirus and antibody after being hospitalized, Chuang said.

The 41-year-old hotel cleaner also worked at Bluejay Residences hotel in Ap Lei Chau and 12A South Bay Road in Repulse Bay. She last went to work there on Sunday and Tuesday, respectively

She is a part-time cleaner at Bridal Tea House Hotel in Yau Ma Tei, a designated quarantine hotel, and last went to work on Thursday.

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A domestic helper from Indonesia stayed at the hotel from June 20 to Sunday before being confirmed infected and sent to the hospital. She was also carrying the L452R strain.

The room was disinfected on Tuesday and cleaned again by the newly confirmed cleaner a day after. 

Health experts who inspected the hotel on Friday afternoon said they believed the room had not been thoroughly disinfected.

Microbiologist and the government’s pandemic adviser Yuen Kwok-yung said the disinfection process lasted fewer than 10 minutes. It was “very undesirable” and not enough to eradicate the virus, Yuen said.

The government said late Friday that around 69,900 Hong Kong residents have received COVID-19 vaccination over the past 24 hours, hitting a new daily high

The cleaner, who has not been vaccinated against COVID-19, may have inhaled the coronavirus particles in the room, Yuen said.

The cleaner also worked at Bluejay Residences hotel in Ap Lei Chau and 12A South Bay Road in Repulse Bay. She last went to work there on Sunday and Tuesday, respectively.

A few of her friends whom she played mahjong with on Sunday and Wednesday at Aberdeen Centre will be quarantined, Chuang said.

READ MORE: HK traces Delta variant infection to 3 imported cases

The remaining 10 new cases reported on Friday were all imported, involving eight arrivals from the United Kingdom and one each from Indonesia and Russia.

The Hong Kong government has banned all flights from the UK, effective on Thursday, in view of the increase in Delta infections there.

The government said late Friday that around 69,900 Hong Kong residents have received COVID-19 vaccination over the past 24 hours, hitting a new daily high.

Hong Kong launched the citywide vaccination drive on Feb 26 and more than 3.84 million doses have been administered so far.

Some 2.31 million people, or about 33.9 percent of the eligible population, have taken at least one shot of the vaccine, and more than 1.53 million people have been fully vaccinated.