Just one day after the country opened a quarantine-free travel bubble with Australia, a New Zealand airport worker tested positive for Covid-19. The border worker works at Auckland Airport, New Zealand's biggest and busiest airport.

The prime minister, Jacinda Ardern, told the press that the worker had been completely vaccinated and had tested positive as part of routine screening early in the launch. She said the worker was cleaning planes arriving from "red zone," or high-risk countries, and that "all signs point" to this case having nothing to do with recent Australian arrivals. It appears that it would have little effect on the newly minted travel bubble between Australia and New Zealand.

Airports in New Zealand are divided into red and green areas. All international flights are routed via the red zones, where passengers are placed in controlled isolation and quarantine. Domestic travelers, as well as those visiting under quarantine-free travel arrangements from Australia, Niue, and the Cook Islands, use the green zones.

These kinds of incidents, Ardern said, were to be expected at the border. “We fully expect people who have been vaccinated to contract Covid-19; it simply ensures that they will not become ill or die.”

If someone who cleans a plane carrying people contaminated with Covid tests positive, she says, “it is by no means a leaky border.”

When the Australian and New Zealand governments announced the bubble laws, Ardern said that cases like this were expected. “This individual was part of our surveillance testing because they worked in an environment that was deemed high risk,” she said. “They're operating on planes coming from high-risk countries.”

When the borders opened, both Australia and New Zealand understood there would be cases on both sides: “We agree that it would be part of our journey together.”

She mentioned that she had not yet spoken with Australian Prime Minister Scott Morrison, but that the health ministers of the two countries were in touch.

She went on to say that, in addition to shielding staff from serious illness, there was evidence that the vaccine "reduces the risk of passing it on to others."

If this is an isolated incident, the trans-Tasman bubble is unlikely to be affected. When the quarantine-free bubble was first revealed, the New Zealand government outlined a "traffic light" mechanism to determine when the quarantine-free pathway will close.

If there was a clear source of an Australian border case and further spread was impossible, the border would remain "green" and travel would continue. The border would be marked "orange" and travel would be halted for 72 hours if a case of unknown origin was likely to be connected to the border. The bubble could close if there were several cases of unknown origin.

“The normal procedure of isolating the case, interviewing them, and tracing their connections and movements is underway,” the Ministry of Health said in a press release on Tuesday, adding that more details will be given later that afternoon.

Officials in New Zealand have previously warned travelers to "flyer beware" and to exercise caution because another outbreak in either country could result in the border being closed. Earlier this month, Ardern said, “We can have situations where travel is shut down one way.” “It can therefore leave travelers stranded on either side of the Tasman for a period of time.”

On Monday, Ardern told ABC TV that 1,800 Australians had crossed into New Zealand.