TAIPEI (BLOOMBERG) - All the virus had to do was get through the border.

Until this week, Taiwan's Covid-19 containment appeared to be so effective that virtually no other defences were put in place: few tests, no local surveillance to pick up undetected infection and close to zero vaccination.

Lauded as one of most successful places in the world at containment, a high level of complacency about the risks had set in among both the public and the authorities. Covid-19 seemed to be something happening only in the outside world.

The virus' opening was an ill-fated decision on April 15 to shorten quarantine for airline crew to just three days, as carriers struggled to operate their cargo lines with staff undergoing 14-day isolation periods.

Infected pilots introduced a more transmissible UK variant, whose spread was then accelerated through a network of "hostess bars" - places both staff and patrons were reluctant to be associated with, making contact tracing more difficult.

Now Taiwan has reported 1,024 local infections in a matter of days - a small number in global terms but an astonishing one in a place that, before May 1, had posted just 1,132 cases during the entire pandemic.

The surge from zero to quadruple digits signals that undetected spread has been occurring for months, and concern is now growing that Taiwan will go the way of other cautionary tales, from the outbreak last year in Australia's Victoria state that took a brutal three-month lockdown to quell, to Thailand's ongoing surge driven by prison clusters.

"If they have 300 diagnosed cases, they have 3,000 cases in the community - they just don't know it," said virologist Gregory Poland, the director of the Mayo Clinic's Vaccine Research Group. "It's going to require a hard lockdown, what's called a circuit breaker approach, and then getting the vaccine out as quickly as they can."

The problem is, there are no vaccines.

As in many places that seem to have eliminated the virus locally, Taiwan's inoculation drive is lagging behind European and North American economies, a major vulnerability that could trap it in a stop-start cycle of restrictions like Singapore, Hong Kong and other regional peers.

Taiwan officials have closed schools, limited social gatherings and urged people to work from home as they try to avoid a hard lockdown, which will be triggered if an average of at least 100 new daily cases is reported for 14 consecutive days and the source is unidentified in half of the cases.

"Be mentally prepared that there will be tougher regulations on activities if community transmission is not under control," New Taipei City Mayor Hou Yu-ih said at a briefing on Monday (May 17). "We are close to another alert level for Covid-19."

Border crossing

The coronavirus' most likely route past border defences was the Novotel hotel near Taiwan's biggest airport, Taoyuan International. Taiwanese exports - in particular semiconductors and other electronic components - are in high demand, and Taoyuan is one of the world's busiest air cargo hubs.

While China Airlines crew members quarantined in one part of the Novotel, another wing was open to members of the public attracted by cheap staycation deals. More than 30 of the recent cases have been linked to the airline and hotel by Taiwan's Centres for Disease Control (CDC), but a clear infection chain is yet to be identified.

It is an illustration of one of Taiwan's key problems. Covid-19 testing has been comparatively infrequent there, a strategy that the Taiwan CDC justified several times last year by saying that mass testing would increase the risk of false positives wasting medical resources.

That is a position counter to global best practices on testing, with most governments more worried about false negatives entering the population and triggering spread.

Taiwan administered 0.18 coronavirus tests per 1,000 people on May 16, according to Our World in Data. In Australia the number was 1.8, while in Singapore, it was 13.1.

Testing is critical because it is the only way to know where and how fast the virus is moving. Increasing testing will be a key step if Taiwan wants to avoid a hard lockdown, said Dr Gigi Gronvall, a senior scholar at the Centre for Health Security at the Johns Hopkins Bloomberg School of Public Health.

"That needs to be a big part of what they do next," Dr Gronvall said. "Even the use of rapid tests are able to quickly identify people who are infectious. That's something that should be deployed and scaled up."

Since its lack of outbreak meant it did not have to keep up with the latest practices in fighting Covid-19, Taiwan did not put in place measures that other places like Singapore and Hong Kong have used to detect asymptomatic carriers.

The high share of infected people who are asymptomatic is a key challenge with the coronavirus and makes containment much harder than with pandemics like the 2003 severe acute respiratory syndrome outbreak.

Infection hot spot

One way to detect asymptomatic spread is wastewater surveillance, which can pick up traces of where the virus is lurking. Another is routine testing of high-risk populations like migrant worker communities or nightlife staff.

In Taiwan, the latter is the nexus of its outbreak.

Many of Taipei's illicit hostess bars are found in the city's Wanhua district, which has become a hot spot for infection. More than 2,000 people had been tested locally as at Sunday, with a positive rate of 10.8 per cent. A rate higher than 5 per cent indicates the dragnet in the search for people who may have been exposed to the virus is not wide enough.

Bars where patrons pay to spend time socialising with escorts known as "hosts" or "hostesses" pose a number of virus risks, as the authorities in Japan have also discovered. These establishments tend to have few windows and poor ventilation, while close contact - including sharing drinks or singing together - can allow infections to spread.

Alcohol consumption makes reckless behaviour more likely, and customers are often reluctant to admit they have visited these clubs, which makes tracing coronavirus cases even harder.

For instance, contact tracing has linked dozens of cases to a past president of Lions Club International, who was later found to have spent time at a hostess bar in Wanhua. "We didn't know the connection to the tea house at first," Health Minister Chen Shih-chung said, using a euphemism for these establishments. He added that the patient only shared the information "after our investigation".

The hostesses themselves are often reticent too. One recent patient was admitted to a general hospital ward for three days with another ailment before staff gave her a Covid-19 test, at which point she admitted she was the boss of a hostess bar.

The question now is how Taiwan gets the situation back under control.

The virus is running rampant among a population where few people have been vaccinated or previously infected. As at Monday, just 0.9 per cent of Taiwan's 23.5 million people had received their first vaccine shot. China has administered enough vaccinations for about 14.5 per cent of its population, while more than one-third of the United States - and more than 30 per cent of Britain - is already fully protected.

It will be hard to ramp up inoculations quickly. Convincing a population that has not felt much threat from the virus to get vaccinated is one issue. But there is also the supply chain. So far, Taiwan has only taken delivery of 315,000 doses of the AstraZeneca vaccine.

Taipei's representative to the US, Ms Hsiao Bi-khim, said in a Facebook post on Tuesday that five million Moderna shots will arrive in the middle of the year, but even that will cover only a fraction of the population.

Central Epidemic Command Centre spokesman Chuang Jen-hsiang said last month that the next batch of AstraZeneca vaccines will likely arrive by June 15, and Taiwan is likely to be a beneficiary of US President Joe Biden's pledge to share millions of doses of US Food and Drug Administration-authorised vaccines with foreign nations by the end of next month.

Meanwhile, officials are hoping that measures like contact tracing and a population highly compliant with public health curbs like mask-wearing can keep spread under control until more vaccines arrive.

It could be a long wait.