Positive test results from anyone who caught Covid-19 from the Sydney tourist in Wellington are most likely to emerge today and Saturday, according to leading scientists.
Ministers will meet on Sunday morning to decide any changes to alert levels, but they will be paying particular attention to test results in the next 48 hours because it would have been six days since Wellingtonians were potentially exposed to the virus.
The Government's precautionary approach continued this evening as it extended the pause on flights to New Zealand from Sydney for a further 12 days, following the four community cases in New South Wales that are not linked to the existing outbreak.
Anyone who has only been in Norfolk Island and not elsewhere in New South Wales is still eligible for quarantine-free travel.
However anyone who was at a location of interest at the specified times cannot travel to New Zealand within 14 days of the exposure event. This applies to all travellers, no matter what Australian State or Territory they are departing from.
Today Wellington enters its second day at level 2, which remains in force until 11.59pm on Sunday, following no positive results today after 2100 tests in Wellington.
"But we know that people can still test negative in those early days after being exposed," said Professor Michael Plank, a modeller at Te Punaha Matatini and Canterbury University.
It usually takes five days after exposure for high levels of virus to show up and return a positive test, he said.
Testing yesterday and today are five days on from Saturday and Sunday, when the tourist visited dozens of locations around Wellington, and the results from those tests will be known today and Saturday.
"Within the next 48 hours, we'll have a clearer picture of whether there has been community transmission," Plank said.
Otago University epidemiologist Professor Michael Baker said if the tourist was "very infectious", some positive cases might have emerged yesterday.
"We won't know till a few days' time if the person wasn't infectious at all."
The tourist had had one shot of the AstraZeneca vaccine, and while there is limited research on the impact of one dose on transmissibility, Baker said it would have somewhat dampened the chances of passing the virus on.
"We've never had a situation where we had one person, potentially infectious and exposed to so many people - it might be more than 1000 - indoors in crowded environments in such a short period of time," he said.
"And we're dealing with the delta variant. There's understandably huge concern about the potential for a series of superspreading events.
"The one thing in our favour is that he was partially vaccinated. We also know that some people were not very infectious at all, and create no ongoing transmission. In fact, a slight majority of cases appear to be like that."
The tourist's partner, who had also received one vaccine dose, has tested negative.
Baker repeated his calls on the Government to make QR code scanning mandatory at high-risk places like indoor bars, and to upgrade the alert level system with a particular focus on mask use to account for aerosol transmission.
Hipkins didn't rule out making QR scanning mandatory in some circumstances, but he said it would be difficult to enforce.
The alert levels in general were under constant review, he said.
"They key is people understand what they are and what is expected. We have seen proposals of seven or even nine different levels and I think that would just become too hard to follow."
He also warned that the vaccine rollout will come under increasing pressure for the next two weeks as stocks run down to empty.
"We have made the decision to run our vaccine stock down to nothing so we can keep the vaccine campaign going," he said.
"We are going to be living for a couple of weeks a pretty hand-to-mouth existence when it comes to vaccines arriving in and us pushing them out as quickly as we can."