HONG KONG (BLOOMBERG) - Hong Kong has detected a suspected Omicron case in an airport cleaner, marking the first time the more infectious variant has jumped through the city's fortress-like border controls and infected a person living in the community who had not recently travelled.

The 64-year-old man who cleaned toilets designated for use by new arrivals thought to be infected with Covid-19 has himself tested preliminarily positive, according to the government statement on Friday (Dec 24). Initial tests suggest he is carrying the Omicron variant, though whole genome sequencing is needed to confirm the findings.

He appears to be the first person in Hong Kong who had not recently travelled and yet contracted the highly infectious Omicron variant. While the Asian financial hub has confirmed 34 Omicron cases to date, all were in people with prior travel history and most were detected upon arrival or in quarantine.

The news comes as lab studies emerge showing that even a booster shot of Sinovac Biotech's vaccine, used by a third of vaccinated people in the city, is not sufficient to protect against the spread of Omicron.

The patient last went to work on Dec 22, the day he developed symptoms. He has no recent travel history and mainly worked in the bathroom used by people who are imported cases while they wait to be transferred to the hospital.

A preliminary investigation showed he likely acquired the infection at work.

Omicron risk

The news underscores the risk of Omicron to Hong Kong, where only 4.3 per cent of the population has received a booster shot, as they are currently only available to high-risk groups. Lab studies from researchers in the city found two vaccine doses from Germany's BioNTech or China's Sinovac are not sufficient to protect against Omicron, which may spread up to 70 times faster than previous strains of coronavirus.

While a third shot of BioNTech's vaccine raises protection to sufficient levels, a third shot of Sinovac's does not, studies found.

The government has locked down the building in Tuen Mun where the airport worker lives to conduct mandatory testing. No positive cases have been found as at 1.30am, after testing was conducted on 1,210 residents overnight.

Other places where he visited in the city during the incubation period have been added to a compulsory testing notice, including multiple restaurants in Tuen Mun, Yau Ma Tei and Tsuen Wan, according to separate statement early on Friday.

The case was likely detected at a very early stage of infection by regular testing, officials said. The worker, who received his second shot of Sinovac's vaccine in August, had multiple negative tests in the past 21 days and low levels of virus present during testing, the government said.

"The most stringent anti-epidemic measures will be implemented to prevent the mutant strain from spreading in the local community," the government said in statement.

The city's stringent snap lockdowns and compulsory testing has proven effective in stopping previous local transmissions. Hong Kong is one of the only places in the world that has yet to experience a Delta outbreak and there has been no domestic virus spread of any variant since early June.

Hong Kong found a Cathay Pacific pilot with Omicron who entered the community last week, and no further cases were found. In August, the city also found an airline lounge staff member who tested positive with the L452R mutant strain, present in the Delta variant.