“Hong Kong will be digging its own grave if it contemplates relaxing its border restrictions at this point,” said Dr Leung Chi-chiu, a respiratory medicine specialist.

“When we already know the mutants can be more infectious, why would we want to gamble away our health and livelihoods in the city?”

Since April 17, the city has recorded three local coronavirus infections carrying an N501Y mutation.

The first was a 29-year-old engineer who arrived from Dubai and is believed to have contracted the South African strain of the coronavirus while in quarantine at a hotel. He is thought to have been infected by two guests on the same floor who were also undergoing self-isolation. 

After his quarantine, the engineer moved in with a friend at her flat in Jordan and infected her, according to health authorities.

On Friday, the third local mutant case was discovered, a Filipino domestic worker who is believed to have contracted the virus while spending her quarantine at a hotel. Two guests in the room next to hers were infected with the variant. 

Explainer | What you need to know about the mutant coronavirus strains in Hong Kong

The quick succession of cases prompted Hongkongers to ask how worried the city should be about the Covid-19 variants, which are believed to spread faster.

Some scientists believe the variant first discovered in South Africa in December, B.1.351, is about 50 per cent more transmissible than the original version of the virus. It has been found in at least 68 countries so far. 

Cases of a second variant identified in Britain in December, B.1.1.7, have been doubling in the United States every 10 days, and it has spread to over 110 countries.

That variant also carries the N501Y mutation, which is thought to be 30 to 50 per cent more infectious, and about 55 per cent more deadly than other variants in circulation.

Both variants, as well as a third that was first detected in Brazil, have been classified by the World Health Organization and many national health authorities as “variants of concern”. 

Hong Kong has so far recorded more than 11,700 confirmed Covid-19 cases. More than 240 carried the N501Y mutation, which is linked to an assortment of variants, though nearly all of those were imported infections detected in quarantine.

‘We don’t know the loopholes’

It was possible for a variant of concern to become prevalent in Hong Kong, said Professor Leo Poon Lit-man, head of the division of public health laboratory sciences at the University of Hong Kong (HKU), whose team collaborated with health officials in decoding genome sequences and uncovering virus mutants in the city. 

Given Hong Kong’s position as a travel hub, he said, it was possible for international travellers to contract variants of concern elsewhere and bring them to the city.

“We can’t say there is no risk, and therefore we must stay alert,” he said. 

Poon noted that despite stringent efforts to prevent imported cases from spreading to the community, including the 21-day mandatory quarantine for overseas arrivals and having designated hotels for self-isolation, there could be gaps yet to be identified. 

“We do not know all the possible loopholes,” he said, adding that they might occur during virus testing at the airport or quarantine in hotels. 

In the latest case of the Filipino domestic worker, Professor Yuen Kwok-yung from HKU suspected she was infected at the hotel where she was quarantined, and contracted the virus through airborne transmission from guests in the next room, two of whom were later found to have the mutant strain. 

Government pandemic adviser Professor David Hui Shu-cheong, of Chinese University, also struck a cautious tone, saying: “Now, Hong Kong is like a goalkeeper … you could miss one or two balls out of 100 shots.”

He said the global spread of the variant first identified in South Africa, for example, showed that Hong Kong faced multiple vulnerable fronts that could be breached. 

Dr Gilman Siu Kit-hang, an associate professor in Polytechnic University’s health, technology and informatics department, was more sanguine. He said the Centre for Health Protection had adopted a “proactive” approach in sequencing the virus genome of all infections, imported or local. 

His own analyses showed that two recent cases from Yau Oi Estate in Tuen Mun, which sparked a cluster of infections, still carried the genome code dominant in the city since its last surge of infections, which began in November. 

“There is no current evidence to suggest the new variants have been circulating or have taken hold in the city,” Siu said.

He explained that mutations were the result of “copying errors” that took place during the process of viruses multiplying themselves. While some errors could make the pathogens more potent, most were just random decoys and some could even weaken the virus. 

But recent research did suggest the variants of concern were “worrying”, Siu said, adding that Hong Kong suffered devastating third and fourth waves of Covid-19 infections after the earlier D614G mutation swept through the city’s institutions, including care homes and hospitals. 

More recently, a variant officially known as B.1.617 has emerged in India, where the Covid-19 situation has turned grim. The strain includes a mutation that might help the virus evade both natural and vaccine-generated antibodies, possibly rendering inoculations less effective.

The country recently logged more than 350,000 infections in a single day, setting the world’s highest daily tally, but scientists are still investigating whether the new strain is driving the surge. 

05:23

Global Covid-19 death toll passes 3 million mark

Global Covid-19 death toll passes 3 million mark

Hong Kong banned flights and travellers from India, Pakistan and the Philippines for two weeks from last Tuesday after the three countries exported five or more mutant infections to the city over a seven-day period. 

Respiratory medicine specialist Leung said the ban should continue beyond two weeks. “It’s simply not realistic [to expect] that these countries can get their epidemic situation under control in a fortnight.” 

PolyU’s Siu added that even after the ban was lifted, the government should send people arriving from those countries to official quarantine centres, rather than quarantine hotels, some of which had become hotbeds for transmissions. 

As for other border control measures, Leung argued that the government’s plan to cut the compulsory quarantine period from 21 to 14 days for fully vaccinated arrivals from countries deemed as medium and high risk – such as the United States, Indonesia and the United Arab Emirates – was a non-starter. 

“There is no evidence suggesting the current vaccines can reduce asymptomatic infections of these mutants or reduce the incubation periods of the coronavirus,” he said. 

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Chinese University’s Hui cited a mainland study last week of the blood samples of people who received the Sinovac vaccine and were exposed to the new variants.

The level of neutralising antibodies in the blood, which defend cells from infections, fell 70 per cent when fighting the South African variant, compared with the Covid-19 strain originally identified in Wuhan. The level dropped 50 per cent for the British variant.

In other similar studies, the neutralising-antibody level in those who had the BioNTech jab dropped 90 per cent against the South African variant, though the level was still above the threshold deemed effective in neutralising the virus. 

Hui has previously said that it remained useful to administer those vaccines in Hong Kong as the variants had not become prevalent yet.

Since the vaccination drive began in late February, about 860,000 people, or 11.5 per cent of the city’s 7.5 million population, have received at least their first dose of vaccine. More than 442,000 of them have also received their second dose.

‘Vaccines are still useful’

Leung said another government proposal for quarantine-free “travel bubbles” with Singapore and other countries should go ahead only if those places have a “symmetrical balance of risk” with Hong Kong, which should now include the number of variants detected and how regularly and effectively they have carried out genome sequencing.

Singapore has recently reported cases of people who were re-infected with Covid-19 after recovering from an earlier infection, and the country has also detected imported cases with various variants.

Hui warned that allowing variants to leak into the community could mean potential outbreaks in Hong Kong, given their higher transmissibility. 

“There will be many more cases because of higher transmissibility. [Staff] at public hospitals would be very busy again,” he said. 

Despite the higher transmissibility of the variants of concern, scientists globally have not yet concluded that the mutants could kill more people.

The emergence of the variants might also affect Hong Kong’s plans for a “vaccination bubble” scheme from Thursday, which allows people to gather in larger groups and stay longer in restaurants whose staff have had their shots.

Poon said those measures would have to be tightened again if a variant chain of transmission emerged in the city.

“The number of people allowed at a table might have to be cut down, or they might be even banned from [dining in] … Control measures will need to be more aggressive,” he said.

Overall, the city had to remain alert to every case, even if it was not a variant, he said, adding: “The fourth Covid-19 wave in Hong Kong was not sparked by any variant of concern.”

While nothing could be done to prevent a virus from mutating, Poon said, the only way to get rid of variants was to wipe out the coronavirus completely, though this could not be done any time soon. 

For now, he said, vaccination remained a useful protection against the virus. 

“Vaccines are not totally ineffective against variants of concern. They could lower disease severity and reduce serious symptoms. Vaccination is a good preventive measure for society,” he said.