Thailand had no new COVID-19 cases for 100 days. Vietnam was the same.

New Zealand, and our neighbour across a different ditch, Timor-Leste tied for first place with 102 days free of new cases respectively.

The coronavirus ability to pop up after months of no community transmission has confounded experts.

It’s pushed cities back into lockdown, sent contact tracers into a frenzy and raised questions about the virus’s ability to survive for long periods.

Until Friday, Thailand had been a success story.

Although it was the first country outside China to record a case of COVID-19, Thailand’s swift lockdown meant it was able to stop the virus in its tracks.

The nation’s contact tracers are currently trying to work out how a disc jockey, who was imprisoned last week, got COVID-19.

Thailand Imposed strict lockdown measures after the country got its first case. Photo: Getty

In August, an unknown source in New Zealand spread the virus to four other Kiwis.

The country now has 152 cases and authorities are still investigating every possible avenue for the outbreak, including that it came in on imported freight.

UNSW epidemiology professor Mary-Louise McLaws said it’s likely in these cases – where COVID-19 pops up seemingly out of nowhere – that the virus has stayed in the community with asymptomatic carriers.

“We do know up to 20 per cent of cases can remain asymptomatic,” Professor McLaws said.

“We’re not sure how important they are at driving an outbreak or spike because they’re often found serendipitously with a family or work cluster.”

Another contributing factor could be that people aren’t getting tested when they need to.

“Not every person acknowledges a change in health due to COVID-19,” Professor McLaws said.

“They may put it down to something else, they may ignore the physical changes.”

A drive-through testing centre in Christchurch, New Zealand. Photo: AAP

“The other reason may be that people aren’t coming forward for testing is because they’re frightened of having to go into isolation and maybe lose their job.”

Professor McLaws said it was an important lesson for Australia because it showed how vital is our response time to outbreaks.

“We’ll always have a risk, the most important thing is how we respond,” Professor McLaws said.

Historically over the course of this pandemic, we’ve responded a bit too late all the time.

“We don’t want a laissez-faire approach to how we’re going to respond when the numbers come up.”

In Timor-Leste, the majority of cases were imported by Timorese students returning from Indonesia, who were all identified and isolated before the disease had the opportunity to spread to the wider community.

But in Thailand, it looks like the case has sprung out of nowhere.

Officials are now racing around the clock to find out how far the virus has spread.

A Timorese policeman enforces a coronavirus rule of just one person per bike. Photo: Getty

Methipoj Chakametikul, head of Bangkok’s disease control division, said authorities were following up with seven high-risk individuals, two of whom had left Bangkok.

“We ordered the closure of his workplaces for three days for cleaning and are investigating his close co-workers,” Methipoj said.

Catherine Bennett, the chair of epidemiology at Deakin University, said the lesson of countries struggling with a resurgence of COVID-19 is to test widely, even after case numbers have dropped.

“Once Australia gets the virus level down, if we’re not testing for people with no symptoms there is a risk that someone will be infectious enough to pass it on,” Professor Bennett explained.

It will be passed along until someone hugs their grandmother, or goes to work at the Meatworks. That’s the risk.”

Only around one in two Victorians with COVID-19 symptoms are getting tested. Photo: AAP

On Wednesday, Victoria’s Chief Health Officer Brett Sutton said he was concerned that around one in two Victorians with cold and flu symptoms were not getting tested.

For Australia to get to zero cases, and stay there for more than 100 days, Professor Bennett said authorities must test everyone, even those with the mildest symptoms.

“Testing is our eyes,” she said.

“The best way for us to manage it when it springs up is to be able to see where the virus is.

“That will help us see prevent mystery cases and manage it so it doesn’t turn into a big cluster.”