ISCHGL ( NYTIMES) - They came from across the world to ski in the most famous resorts of the Austrian Alps.

Mr Jacob Homiller and his college friends flew in from the United States. Ms Jane Witt, a retired lecturer, arrived from London for a family reunion. Ms Annette Garten, the youth director at a tennis club in Hamburg, Germany, was celebrating her birthday with her husband and two grown children.

They knew in late February and early March that the coronavirus was spreading in nearby northern Italy and across the other border in Germany, but no one was alarmed. Austrian officials downplayed concerns as tourists crowded into cable cars by day and apres-ski bars at night.

"The whole world meets in Ischgl," Ms Garten said.

Then they all went home, unwittingly taking the virus with them. Infected in Ischgl (pronounced "ISH-gul") or in surrounding villages, thousands of skiers carried the coronavirus to more than 40 countries on five continents. Many of Iceland's first known cases were traced to Ischgl. In March, nearly half the cases in Norway were linked to Austrian ski holidays.

Nine months into an outbreak that has killed one million people worldwide, Ischgl is where the era of global tourism, made possible by cheap airfares and open borders, collided with a pandemic. For decades, as trade and travel drew the world closer, public health policy, enshrined by treaty, encouraged global mass tourism by calling for open borders, even during outbreaks.

When the coronavirus emerged in China in January, the World Health Organisation (WHO) didn't flinch in its advice: Do not restrict travel. But what is now clear is that the policy was about politics and economics more than public health.

Public health records, scores of scientific studies and interviews with more than two dozen experts show that the policy of unobstructed travel was never based on hard science. It was a political decision, recast as health advice, which emerged after a plague outbreak in India in the 1990s. By the time Covid-19 surfaced, it had become an article of faith.

"It's part of the religion of global health: Travel and trade restrictions are bad," said professor of global health law Lawrence Gostin at Georgetown University who helped write the global rules known as the International Health Regulations. "I'm one of the congregants."

Covid-19 has shattered that faith. Before the pandemic, a few studies had demonstrated that travel restrictions delayed, but did not stop, the spread of severe acute respiratory syndrome (or Sars), pandemic flu and Ebola. Most, however, were based on mathematical models. No one had collected real-world data. The effect of travel restrictions on the spread of the latest coronavirus is still not understood.

"Anyone who is truthful is going to tell you it's a big fat 'We don't know'," said Professor Keiji Fukuda, a former senior WHO official who teaches at the University of Hong Kong.

Not knowing is especially vexing as the world seeks a way back to normalcy. For months, national leaders have invoked travel restrictions that vary in strictness and are often contradictory. Some shut their borders and simultaneously imposed domestic lockdowns. Others required tests and quarantines. Many regularly revised their lists of risky destinations, sometimes responding tit for tat when their citizens were denied entry.

The restrictions have humbled powerful nations like the US, whose citizens are no longer welcome across most of the world. Even so, President Donald Trump has called his travel restrictions "the biggest decision we made so far" and attacked the WHO's early advice on borders as "disastrous". Still, it is too soon to know, based on data and hard science, how much travel restrictions help and, if they do, which restrictions help most.

Experts who had defended open borders at the start of the pandemic now say countries should use judicious travel measures. The WHO now calls for a gradual reopening in which each country weighs its own risks.

"There is certainly a stark shift in how it's being discussed," said Professor Kelley Lee at Simon Fraser University in Canada who is studying the impact of travel restrictions in this pandemic. "But the evidence hasn't changed. We still have poor evidence." What is vividly clear is that global public health policies are inadequate, especially regarding travel. Low-cost airlines have created a surge in global travel. The number of people taking at least one overseas trip a year has grown by 80 per cent since the regulations were formulated in 2005.

The ease and expansion of global travel is why "superspreader" events helped accelerate the pandemic: Just as skiers in Ischgl carried the virus around the world, congregants at a French megachurch took the disease to Africa, Latin America and across Europe.

After his trip to Austria, Mr Homiller and at least four friends tested positive for the coronavirus. Ms Witt buckled from exhaustion in her kitchen and ended up fighting for her life. Ms Garten's family became sick, too, and in Germany, her husband was hospitalised.

Now at least 1,000 people from dozens of countries intend to sue the Austrian government. A lawyer in Vienna filed the first test cases recently on behalf of four visitors, two of whom have since died of Covid-19. The lawsuit says the government should have closed the resort earlier and told tourists to stay away.

"They knew; they just weren't telling anyone," said Ms Witt, who is part of the lawsuit. "Wealth before health."

PLAGUE AND PANIC

Growing up in Hamburg, Ms Garten was 16 when her family first visited the sleepy resort of Ischgl in the late 1980s. It catered to avid skiers, mostly Germans. Cow manure sometimes littered the streets. "It was a normal Austrian village," she said.

The village became a resort in the 1960s after an enterprising resident went door to door collecting money for a cable car. When Ms Garten visited, it was hardly on the global tourism map. That began to change in the 1990s, when Ms Garten started spotting Britons on the slopes and Russians in big furry hats. New hotels rose along the narrow streets. Stars like Elton John and Bob Dylan headlined concerts.

The same forces of globalisation reshaping Ischgl were transforming the world. Multinational companies embraced outsourcing and international supply chains. Global trade made countries interdependent, which also came with risks.

In the fall of 1994, a plague outbreak struck the Indian port city of Surat. Hysteria erupted, and countries quickly banned travel to India. Tourists abandoned their vacations. Airlines cancelled flights. The United Arab Emirates banned Indian cargo, while Russia demanded quarantines on shipments.

Plague is not uncommon, with small outbreaks every year, even in the US, and Surat's outbreak turned out to be relatively mild, with just over 50 deaths. But the global panic devastated the city and cost India's economy an estimated US$3 billion.

The reaction to the outbreak alarmed Professor David Heymann, an American epidemiologist who was then a senior WHO official involved in the agency's response to Surat. Indian officials had properly reported the outbreak and quickly brought it under control. Yet India was punished, a response he considered "irrational". "It had nothing to do with the outbreak," said Prof Heymann.

At the time, the International Health Regulations were designed to prevent trade interruptions. But they applied to only three diseases: plague, cholera and yellow fever. Enforcement was impossible, and countries often implemented arbitrary travel bans for other diseases.

Surat exposed the most glaring blind spot. The world's pandemic alert system depended on political leaders to sound the alarm. If financial ruin was the cost, no country would report an outbreak.

"That really made us realise that the regulations had to be changed," Prof Heymann said.

The WHO soon undertook a broad reassessment of the rules, but the revisions ground slowly until the Sars epidemic hit in 2003. Fearing a pandemic, the WHO advised against travel to affected countries, the most stringent recommendations in its 55-year history.

Most of the affected countries were in Asia, but it was Canada that felt most aggrieved after the WHO advised against travel to Toronto. Then, WHO member states gathered during the Sars epidemic and told the agency to complete the revisions.

This time, the process was swift. In 2005, diplomats struck a compromise intended to balance public health needs with the economic consequences of "unnecessary interference" with travel and trade. While the new rules did not explicitly prohibit countries from closing borders or restricting trade, they made it clear that doing so should be a last resort. But the rules were never based on a scientific body of evidence. There were reasonable assumptions: Closed borders could slow the arrival of medicine and aid workers, for example. Yet, no one studied whether restricting travel might slow a fast-spreading disease, partly because there was no tradition of collecting data on such interventions.

"We didn't think we needed to measure them because we thought we knew," said Prof Gostin, who was involved in the revision process. "Clearly, we didn't."

The new rules took effect in 2007 even as the world was rapidly making them obsolete. Focused heavily on trade, they failed to account for "a tourism industry that grows out of bounds", said Professor Ilona Kickbusch at the Graduate Institute of International and Development Studies in Geneva.

By the 2000s, Ischgl's nightlife had earned it the nickname of "the Ibiza of the Alps". Huge parking lots had been built for a stream of buses from across Europe. More significant, though, was the impact of low-cost air travel.

Today, tourists can reach Ischgl from eight nearby airports in Austria, Germany, Switzerland and Italy. One of them, Memmingen Airport in Germany, was once a military airfield whose rapid transformation began when Ryanair, Ireland's low-cost carrier, started flying there in 2009. The airport now serves several budget airlines and had more than 1.7 million passengers last year.

Over the past decade, flights via Munich and Zurich have brought tourists from as far away as America and China, and Ischgl today hosts 300,000 tourists from 36 countries every year. This winter, Ischgl's hotels were full, even as ominous reports were emerging from Italy.

Ms Garten said she never worried. She laughed when her boss warned her not to bring back the virus. "I thought, we are going into the mountains; we will be outside in the fresh air," she said. "What could possibly happen?"

A FRANTIC EXODUS

Ms Garten comes to Ischgl to ski and rarely goes out, but she made an exception the night before her 50th birthday. When she arrived at the Kitzloch bar with her husband and some friends, the floor was packed, and the music thumping. Drunk patrons danced in ski gear. Servers blew whistles - twice into her face - to part the raucous crowds. "I just remember the whole experience as being very wet," she recalled.

That night, March 5, Iceland issued a warning against travel to Ischgl after more than a dozen returning travellers tested positive. Two days later, a German bartender at the Kitzloch became the first Covid-19 case confirmed in Ischgl, yet local officials reassured guests that all was well.

"From a medical point of view, transmission of the coronavirus to guests in the bar is rather unlikely," a provincial medical director said in a statement the next day.

The Kitzloch was disinfected and reopened for business.

The day after that, its entire waiting staff tested positive. Mr Bernhard Zangerl, the 25-year-old manager, blamed "bad luck" and chafed at accusations of negligence.

"The virus is not from Ischgl," said Mr Zangerl, who was also infected. "It was brought here." By then, though, Europe's system of seamless travel was collapsing. An overwhelmed Italy had closed its borders. In Vienna, Austrian leaders struggled to respond to an upended world.

"Only a few weeks earlier, we had looked at China and told ourselves, 'Such a quarantine is only possible in China'," said Austria's Health Minister Rudolf Anschober. That month, he said, his government had to make decisions that he had once found "impossible to imagine". The Kitzloch closed, but other bars stayed open another day, even as warnings poured in from the rest of Europe.

Finally, the provincial governor, Mr Gunther Platter, announced that the winter season would end early in the entire province, rather than risk allowing another 150,000 guests to arrive the coming Saturday. "It meant that €1.5 billion (S$2.4 billion) was gone," he said.

Mr Platter said his province had no guidance because organisations like the WHO and Germany's Robert Koch Institute were slow to react. At the time, Mr Platter said, he felt like he was going "too far, too fast". Mr Peter Kolba, the Viennese lawyer who is leading the litigation against the Austrian government, argued that the valley should have been closed a week earlier, after the first few cases had been linked to Ischgl. It remained open only because officials were interested in tourism, he said.

"Every day is precious in the winter season, especially in Ischgl, where people spend a lot of money," Mr Kolba said.

Once Mr Platter decided to shutter the resorts, local officials quickly drafted an evacuation plan. Foreign tourists would leave, while Austrians and seasonal workers would be quarantined. But before it was made public, Austria's Chancellor unexpectedly announced the shutdown on television.

Everyone scrambled to leave.

Ms Witt, the retired lecturer from London, saw shopkeepers hastily locking up in the nearby village of St Anton. Her daughter, who was still skiing, noticed ski-lift operators abandoning their posts.

"Within an hour, there was nobody on the street," Ms Witt said. "It was frightening." The valley's main road was clogged with honking cars. Police could not collect contact-tracing forms from many departing tourists, leaving their home countries blind to the dangers heading their way, according to Mr Kolba.

At least 27 tourists died after contracting the virus in Ischgl, St Anton and neighbouring towns, Mr Kolba said. More than 11,000 Europeans were infected in Austria, many of them in Ischgl and adjacent resorts, research by Austria's public broadcaster ORF showed. Researchers from the University of Innsbruck tested 1,500 Ischgl residents in April and found that 42 per cent had antibodies for the virus.

A VERY UNCERTAIN FUTURE

Mr Andreas Steibl, the jovial, quirky director of Ischgl's tourism board, has little doubt the resort will recover. Some tourists, like Mr Homiller, are determined to return.

"We should go back," he said. "Even though a bunch of us ended up sick, it was a great week." Yet, infections are on the rise, and no one can say what the world will look like when ski season begins next month. Returning to a world of unimpeded travel seems hard to imagine, at least for now.

As scientists worldwide race to make a vaccine, understanding the role of travel in a pandemic - and what types of restrictions could prove effective - is also critical, if likely to take much longer. This month, the WHO began another review of the International Health Regulations.

Prof Heymann, who helped shape the last revision, acknowledges that the current regulations "are not fit for purpose on travel and trade". "More and more," he said, "we're understanding that there are some times when travel and trade might need to be restricted."

Still, experts like Prof Gostin fear that in the absence of data, the world will over-correct - only to find during the next pandemic that new restrictions have slowed access to medicine, delayed rescue workers and needlessly damaged fragile economies.

"If we're going to make choices that affect the world so profoundly, we need to understand if they work," he said. "Otherwise, we're just flying blind."