A health worker takes a swab from a woman at a COVID-19 testing centre setup outside the immigration headquarters in Hong Kong on April 24, 2021.

HONG KONG – Genetic sequencing has failed to link conclusively the case of a variant-infected 17-year-old Hong Kong girl to any of the city’s recent imported cases.

The student contracted the Alpha variant strain first discovered in Britain and her infection was confirmed on Saturday, ending the city’s 42-day streak of no cases with an untraceable origin.

Her 20-year-old sister and their mother were also infected. The Centre for Health Protection confirmed the infection of the student's sister with the Alpha variant, one of the seven new cases reported on Monday. The six other infections were imported from Indonesia, the US and the United Arab Emirates.  

The student contracted the Alpha variant strain first discovered in Britain and her infection was confirmed on Saturday, ending the city’s 42-day streak of no cases with an untraceable origin

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The genome of the teen’s strain was also not similar to infections in a Shenzhen district, where a number of patients carrying the Alpha variant were reported, the Centre for Health Protection said in a statement.

“The CHP’s epidemiological investigation of the case is ongoing and further genetic analysis and comparison with recent imported cases with N501Y mutant strain are continuing,” reads the statement.

The Hong Kong government also announced on Sunday night the suspension of quarantine exemption for residents returning from medium and high-risk areas in Guangdong province, including parts of Guangzhou where small-scale outbreaks have been reported with residents being restricted from leaving.

The Alpha variant is particularly predominant in Taiwan and Indonesia at the moment.

In addition to following the guidance of National Health Commission, the government said it will also review the reported cases on the mainland to finetune the city’s quarantine-free Return2HK program.

READ MORE: HK reports 1st untraceable case with COVID-19 variant

As of Sunday, nearly 1.53 million Hong Kong residents, or 23.3 percent of the city’s entire population, had received at least the first vaccine shot, while 1,109,407 people had been fully vaccinated.

Hong Kong reported seven new COVID-19 cases on Sunday, including one involving the teenager's mother. The city's tally stands at 11,865.