AMSTERDAM (NYTIMES) - For the hundreds of passengers travelling from South Africa to Amsterdam on Friday (Nov 26), flight KL592 had all the trappings of international travel in the Covid-19 era.
They came armed with paperwork proving their eligibility to fly, and check-in agents sifted through a bewildering assortment of requirements determined by final destination.
Some countries, such as the United States, required vaccinated travellers to show negative test results. Others didn't. On the long flight, only some wore masks, passengers said, as flight attendants often let the slipping masks slide.
But while the flight was en route, and the passengers slept or watched their screens, everything changed on the ground.
Panic about the new Omicron variant that had been discovered in southern Africa prompted countries to close their borders.
The arrivals descended into a new post-Omicron reality, and it was a hellish one, with hours spent breathing stale air as their planes sat on the tarmac, then fighting exhaustion in crammed waiting rooms, awaiting swab results in close quarters with fellow travellers who would turn out to be infected with the new and possibly more dangerous variant.
"We were in the same place, the same room," said one passenger, Mr Jan Mezek, 39, a laboratory technician whose company services swab-test machines and who was returning from a two-week work trip to his home in Prague. "I felt like a pig in a pen," he said, adding "they were completely spreading the virus around us".
Of the more than 60 people on that and another KLM flight from South Africa who tested positive for the virus, at least 14 had Omicron, according to Dutch officials.
The Dutch authorities have quarantined them - and arrested a couple who had tried to break out and fly to Spain - while requiring the hundreds who showed negative results from the polymerase chain reaction (PCR) test administered at the airport to go home or board connecting flights to their final destinations.
"They went around the world, who knows where," said Dr Fabrizio Pregliasco, a prominent Italian virologist at the University of Milan.
He said that all the passengers should have been quarantined or isolated and monitored closely for seven to 10 days, especially because they could have caught the virus on the flight and tested negative as it incubated.
"If this variant is very contagious, this flight is an explosive bomb," Dr Pregliasco said.
The flights, like the cruise ships of the early pandemic, have prompted fears of super-spreader events and raised concerns about lessons unlearnt.
But they are also emblematic - with the varying testing and quarantining criteria, the inconsistent mask wearing and confusion over contact tracing - of the scattershot global response, and often lax enforcement, that may worsen a possibly more infectious stage of the pandemic.
The Omicron variant, though designated "very high" risk by the World Health Organisation, is still an unknown variable. It will probably take weeks to know if it amounts to an overblown scare or a highly contagious new mutation with the ability to dodge the vaccines and potentially plunge the world back into lockdowns, packed hospitals and unattended funerals.
The security conferred by the vaccines and by planes with air filtration systems led the United States to open up to European Union travellers and other nationalities earlier this month, allowing for embraces, tears and giddy reunions long denied.
But European countries had different rules from those in the US - and often from one another - about the testing and self-isolation criteria required for vaccinated people to board a flight. The result was an often shifting patchwork of regulations by countries.
The rules for any given passenger on any given flight are generally determined by that person's final destination country, said Dr Karen Grepin, a professor at the School of Public Health at the University of Hong Kong, who has been studying travel rules during the pandemic.
Countries and often airlines have their own testing requirements, and transferring passengers sometimes have to meet still different criteria.
The result is that a passenger in an aisle seat may have been tested differently from the passenger across the arm rest. The US has required all inbound travellers to show proof of a negative test before boarding their flight.
Responsibility for navigating this warren of information often falls to the gate agent, who once checked passports and luggage weight but who now must be knowledgeable about dozens of different travel regulations on any given flight.
Already the target of traveller frustration, gate agents have said tensions with passengers have worsened as the agents have been asked to essentially fill the roles of border guards, health inspectors and consuls.
But all that confusion and agitation may soon seem like the good old days, when travel, if confounding, was at least possible.
After the emergence of the Omicron variant in Africa last week, the US and the European Union and other nations banned flights from southern Africa.
Israel and Morocco slammed their doors on the world. Australia, Japan and other countries postponed opening up and joined China, which has adopted a fortress mentality as it seeks to vanquish the virus at home altogether.
For all the focus on the flights to the Netherlands, positive cases of Omicron have already emerged in several countries and public health experts consider its emergence everywhere inevitable.
A vaccinated Italian, who has not been publicly identified, returned from business in Mozambique earlier in November to the southern town of Caserta. He said on Italian radio that he had tested negative before boarding his flight on Nov 11, as was required by Italy. Since he was travelling for work, he did not, per Italian rules, have to self-isolate upon return.
It was only during a medical check-up in Milan, where he also underwent a Covid-19 test so that he could return to Mozambique, that he tested positive for the coronavirus, and then, amid the heightened attention to the new variant, for Omicron.
Now he and his wife and children, who are also positive for the virus, are in isolation, all for now with light symptoms.
On Tuesday, KLM, the airline which operated the two flights last Friday from South Africa, apologised to passengers. But Ms Marjan Rozemeijer, a spokesman for the company, suggested it had been just as caught off guard by the variant as anyone.
Upon the landing of the flights at Schiphol Airport, she said, the company was "asked by the Dutch government to park our aircrafts in a particular location so that all passengers could be tested", and added that the airport and the Dutch public health authorities had organised and performed the testing.
A spokesman for the Dutch public health service, by contrast, said it had gone above and beyond in its efforts and saw nothing wrong with letting the passengers who had tested negative for the virus proceed on their journeys.
"There is no reason why we should restrain people from travelling if they have a negative test," said Mr Willem van den Oetelaar, a spokesman for the Public Health Services of the Netherlands, which said it followed Health Ministry guidelines. "We don't know where the passengers went and see no reason why we should know."
But the Dutch Health Ministry said even the passengers who tested negative should be in quarantine, and Mr van den Oetelaar said the agency had taken the extraordinary step, usually reserved for reaching out to passengers in the vicinity of an infected person, of trying to contact everyone who was on the planes and urging them to quarantine and notify their local health authorities.
The World Health Organisation, which has been closely monitoring the new variant, said that international contact tracing was up to countries where cases were detected and fell outside its purview.
Mr Mezek, who is vaccinated and tested negative, said he had received a call from the Dutch public health service on Saturday, and then an e-mail imploring him to stay home and supply it with his travel details after leaving the Netherlands.
"It is important to know your whereabouts, so that health departments in various countries can contact the transfer passengers, to prevent further spreading" of the Omicron variant, according to an e-mail shown to The New York Times and verified by the health agency.
It added that he should be tested again for Covid-19 five days after the South Africa-to-Amsterdam flight's arrival. "Although you may not currently have any symptoms, you could already be infectious."
Mr Mezek said he was in isolation, and had already received a call from the Czech authorities on Monday making sure he was staying put, and not sick. But he noted that if he had made his original connection, and landed a day earlier, before the Czech Republic tightened its rules, he would be at work and at home with his children and wife, a teacher.
"I wouldn't have been in isolation," he said.