An infectious diseases expert says if Jacinda Ardern called her for advice on whether to lift COVID-19 restrictions, she'd tell her to keep them on - even though there's no evidence yet of any further transmission of COVID-19.
Auckland has been under alert level 3 since Monday after three cases of the highly infectious UK variant were picked up in the city's south. Thousands of people have since been tested for the virus, including dozens of close contacts, but all have thankfully come back negative.
"We have to remember the incubation period is usually around two to 10 days for most people, but some people can be about 14," microbiologist Siouxsie Wiles told The AM Show on Wednesday.
"The test that people have is a point-in-time test - at the time when they were tested and they were negative, that's great. But if they're a close contact they could still be within those 14 days and test positive in a few days' time.
"It's good news that we haven't had any positives yet, but that doesn't mean that we might not have any pop up in the next few days."
Nearly 6000 tests were carried out on Monday, the Ministry of Health reported at 1pm on Tuesday. New tests done overnight have also come back negative, COVID-19 Minister Chris Hipkins told The AM Show.
"If there had been some spread, we would expect to see somebody test positive hopefully," said Dr Wiles. "But we know there are lots of test results not back yet. I really hope they're all negative but we do have to remember that just because they were negative doesn't mean they might not become positive in a few days' time."
The last time community cases were found in Auckland there was no lockdown, because the source was quickly identified. Genomic testing hasn't been able to link these latest cases to any previously found in the country.
"It is a worry not knowing the source - that's why the wide net's been cast. What we're concerned about is there might be some transmission chains out there that we haven't identified yet."
That's why Dr Wiles doesn't think the alert levels should shift just yet.
"I'm really glad I don't have to make that decision - obviously I'm just thinking from a health perspective.
"It's also about whether we want to yoyo in and out - my advice would be we stay a couple of days and see what happens. The last thing we all want is to come out of alert level 3 then need to go back into it again next week because we have detected some cases. That's the thing that will be being weighed up at the moment."
Even a single person out there with the virus could inadvertently cause a major outbreak, Dr Wiles says - hence the cautious approach.
"You know the 80/20 rule? Basically with this virus about 80 percent of infections are caused by 20 percent of people. Some people don't go on to infect anybody, or maybe only infect one person; then you have other people who are involved in these superspreader events where you can end up with tens or hundreds of people infected.
"That's the worry - if there are some people out there that aren't detected, once we move back to alert level 1 and we're all meeting in large gatherings and things, there's then that potential for a super-spreading event. That's why it's really frustrating - it's not as simple as 'if this person's infectious then naturally somebody else will get infected'. It just doesn't work that way."
New Zealand's vaccine rollout is set to start on Saturday, beginning with frontline border workers. There has been a decline worldwide in the number of confirmed new cases being reported each day, including in the hard-hit UK. Dr Wiles says it's too soon to credit the UK's vaccine rollout for the drop.
"The idea that the vaccine has contributed to the UK's drop in cases is unclear at the moment. You have to remember they've been in a lockdown since the beginning of January."
The UK has also focused on getting as many first doses into people's arms as possible, hoping at least some protection will be better than none. Most of the vaccines developed to date - including the Pfizer-BioNTech vaccine, the first out of the gates - need two doses to reach their maximum efficacy.
It's a risky move, says Dr Wiles.
"We're only going to find out once they start lifting restrictions what impact that one dose of the vaccine has had. My worry - and this is certainly a worry of many of the experts in the UK as well - is that if people haven't got both doses and don't have a good enough immune response, and you open up (and we know they're going to open up while they still have lots and lots of infectious people) you may be providing a training ground for the virus to evolve to basically escape the immune response.
"That would be a really quite devastating thing."
Luckily the Pfizer-BioNTech vaccine - the one we'll be rolling out first - appears to be effective against the fast-spreading UK variant, based on early data from Israel's rapid rollout.