HONG KONG : The sudden re-emergence of Covid-19 in places with the world's best records for handling the pandemic is sending a discouraging message to health officials: Strategies to fully snuff out the virus don't work as a long-term solution, and even the most successful places can never let down their guard.

After more than 250 days without a single locally-transmitted coronavirus infection, Taiwan reported its first case since April on Tuesday (Dec 22), ending what was the world's longest virus-free streak.

On the same day, Thailand saw 427 new cases, a staggering jump for a country that as recently as September had gone 100 days without a domestic infection.

"Unfortunately, in countries that have got really low levels of virus and may well have eliminated it, it's so easy to come back," said professor Peter Collignon, a clinical medicine expert at the Australian National University Medical School in Canberra who has advised the country on virus mitigation.

"My worry is when you use the term elimination, people think it's gone, and so they can go back to their normal activities and not take any restrictions."

The Asia-Pacific region has largely avoided the unbridled outbreaks that continue to dog the United States and parts of Europe, but the pandemic's persistence elsewhere means it can be reintroduced to places that have quelled cases locally even with border curbs and mandatory quarantines in place.

The Taiwan case was in a woman who came into contact with an airline pilot recently arrived from the US, while a flare-up in Sydney - which had also gone months with just a few local infections - may have originated in a hotel quarantine worker.

These re-emergences come as other parts of the region lauded for their virus control also come under pressure with the onset of winter.

South Korea and Japan had managed to keep cases at a manageable level for most of the year without resorting to lockdowns or the sorts of restrictions seen elsewhere. They're now seeing record infections as that strategy is challenged by people's fatigue with the pandemic and their migration indoors with the colder weather.

Countries that have succeeded in achieving minimal or no transmission may actually need to employ much more rigorous controls in order to keep cases close to zero, Prof Collignon said.

That's been the strategy in places like China, Australia and New Zealand, which have instituted some of the strictest measures to stamp out flare-ups.

Life in these countries has largely normalised, though masks are still worn in places like Beijing and Australians are banned from travelling overseas.

Rather than aim for complete eradication, Prof Collignon said, it may be better to try for maintaining infections at low levels.

That way,"you still keep the general population adhering to physical distancing, keeping away from work when they're sick, keeping away from family when they're sick and wearing masks, as it looks like there's community transmission", he said.

The coronavirus crisis will linger for another two to three years, according to Prof Collignon, even with the rollout of vaccines, which he notes are probably more effective at preventing disease in the vaccinated person than in stopping its spread.

"You may be reasonably safe in your own country," he said. "But as soon as you travel, you still have a risk."

The potential for renewed community outbreaks threatens to tarnish some of the standout virus success stories so far.

Taiwan holds the No. 2 spot in Bloomberg's Covid Resilience Ranking, a measure of the best places to be in the Covid-19 era, while Thailand is 14th of 53 economies evaluated. New Zealand, which has openly said it is pursuing an elimination strategy, comes in first.

The re-emergence of the virus may see some restrictions on movement in these places return.

Right before the resurgence, Thailand relaxed restrictions on visitors from 56 countries, including the US, Japan and Singapore, in an effort to boost the nation's ailing tourism sector ahead of the peak holiday season.

Taiwan said on Wednesday it will look into tightening control measures for flight crew.

In South Korea, whose elite testing-and-tracing practices have become a global model of best practice, health officials conceded the latest outbreak has been particularly challenging to combat as small clusters of infections are more widespread and sprouting across the country.

"The virus is with us forever now and it will not be eliminated," said Professor Nigel McMillan, director of the infectious diseases and immunology programme at Griffith University's Menzies Health Institute Queensland.

"It's a matter of continual testing, contact tracing and isolation of close contacts, quarantine of incoming international visitors, sailors and air crew," he said.

"Vaccination will ultimately turn this disease into something like influenza."

  - Bloomberg